General Guidelines

Introducing Nova

If I had to introduce Nova in a few words, I'd say:
Nova is a cloaked ranged assassin with a low health pool and a high burst.
This says pretty much everything, but every part of this has to be fully detailed. People see Nova as a useless hero who kill noob teammates because they're obviously noobs. There's a lot more to her than this. Even though she doesn't seem viable at pro level, the good news is, she's viable in Hero League from rank 50 to rank 1. If you're reading this, chances are you are not a pro, so why would you care about pro picks?

Playing Nova

One thing to keep in mind is to be efficient all the time. If we talk about mechanics only, Nova can do two things efficiently: bursting a target (preferably a hero), moving quickly around the map without getting spotted. Even if your speed is the same as the other heroes, minions don't hit you when you switch lanes so you're actually faster. Everything else she does poorly. Don't waste time doing what Nova can't do well.
One other thing to keep in mind is to balance risk and reward. Just ask yourself: "Will I kill him if I pick him now ?". In most case if you don't kill him within 3 seconds, you're the one who's going to die. A huge part of your job is knowing if you can or cannot kill this hero.
Lastly, Nova's a lot about mind games. Hiding, using holo decoy and nuking are all parts of interesting mind games. We'll detail all of that in this guide.

Everyone hates you

You're going to play with one of the most hated hero in the whole game. Your opponents hate you and take pride in killing you. You're a mosquito, you're hard to spot, you sting, everyone hates you but you die quickly. You're an annoyance to them and they'll jump at you hard as soon as they can. You can use that (see holo decoy section).
Most annoying to you is that your teammates hate you too. A lot of people pick Nova because she's in Starcraft 2 and she's gorgeous. I did that too and I sucked. You'll get a lot of hate in Hero League lobby, even then try to be constructive, most people actually can understand when you talk to them. Anyway if she's a good pick (good map for her/good opponents for her/your team composition allows you to pick a ranged assassin), you can grab her against the team's will (see when to pick Nova section).

Nova's do

The order doesn't matter, except for 1. It's the greatest priority.
1. Don't die. At all. It means, most of the time you won't even be able to help endangered teammates and you'll often have to let them die. If you're 100% sure you can help without dying, do it.
2. Finish hurt heroes after a fight. Securing a kill on a retreating 10% HP hero is your job. If the enemy can just back and heal, you are not doing your job. You can chase during the fight only if your team can win it without you (it's often the case, you're not a sustained DPS).
3. Gank heroes, pick up weak/hurt heroes in lane. You're hard to see, so abuse it to catch unsuspecting heroes. In lane, specialists often over commit because it's their job to push, even early game. Your best target here is Sylvanas. Most Sylvanas won't leave their lane even at 20% HP. Your job is to punish them.
4. Scout, roam around objectives, opponent merc camps and so. You'll give your team map control, you'll find kill opportunities, and best of all you'll acquire a good map awareness as a player in the long term. Giving vision to your team mustn't be underestimated. Sometimes it's better to give vision on the other team than actually helping with the merc camp or boss. If you know how or when the enemy is going to jump at you, you can actually counter their gank and wipe them.
5. Mount. All the time. A lot more than with other heroes. Since you shouldn't use your attacks and spells on anything else than enemy heroes, you'll have to at least be mounted, ready to act fast.

Nova's don't

1. Die. Always balance your risk/reward. If you engage an isolated hero make sure that: you won't die (always your 1st priority), and it's even better if he dies.
2. Lane, waveclear. I'd say 75% of the time it's a bad move. You have the worse waveclear ingame after Slapathur (not counting hat and mines, just the slapping with the little creep spawning automatically). If your team forces you to lane by roaming themselves or stupidly going for camps at wrong times, try to explain it to them. If you feel you have no choice, stay under your towers and shoot all you got. It'll take forever and you're not doing your job. Worse, you're wasting mana, meaning you'll have to hearth back quickly.
3. Take objectives. You have to be in front giving vision to your team while they're trying to get the objective. You can't do that if you're grabbing the tribute. Of course if you're the last man standing, or your whole team is chasing them and you're behind for some reason (respawn morst likely), you have to get it. But it's rare.
4. Waste your mana. Nova is quite the mana hungry hero. Most of the time when you use a fountain you're full health but it's to get mana. You must at least have enough mana to shoot all your spells once, and twice at level 20. Since you'll be roaming, if you have a Malfurion with you be sure to ask him for mana often.

Learn to chase

There'll be one "skill" you'll need to learn, it's how to mount properly as a cloaked hero. It's mostly about lane situations, but it applies anytime you might get uncloaked / unmounted by any damage source.
Let's sat you're in lane and you have to mount to chase. There is a full minion wave in front of you. Mounting will uncloak you and then you have 3 seconds "to wait" before being cloaked. During these 3 seconds you mustn't take any damage. So instead of rushing to chase your opponent you'll want to avoid the arched/mage minions or whatever may hurt you and the instant you cloak step in their range to chase as fast as possible. It may seem easy, or obvious, but doing it well really takes practice. While you delay your chase you may want to show your opponent you're backing. You're not of course but they may lower their guard.
It's the same every time you want to switch lane, if you head to one direction while being spotted, change as soon as you cloak to confuse them (if your opponents are good enough to look at the map often).

To chase efficiently you have to know when an hero is backing, and anticipate what he'll do. Knowing if he'll go to the fountain, or just back behind the first doors or mount to his core is the difference between getting a free kill and getting none. You'll be wrong more often then not. My friend always teases me because I always say in vocal chat how dead this one is gonna be and I really succeed less than 50% of the time (most of the time I've picked the wrong option and simply don't find him). That's still a lot of free kills.
All maps allow you to roam behind the fort from the beginning of the game. No map allow you to roam to the keep without destroying at least 1 building. That doesn't mean you can't get a kill even by staying outside the wall (see holo decoy section).

For all these examples I'll consider you chased efficiently but are out of time. It's almost always the case. Let's start by saying that any hurt hero that backs and tries hearthing in lane or in bushes versus Nova or Zeratul is dead. If you just pay attention to who's injured and who's not, you almost always notice him and go get the free kill. You don't need a guide for this.
The first thing to do is to watch the small orange bar that shows the hearthing progress. It'll tell you how much time you have before he teleports.
Also, a base rule is that you go there to get a free kill and you mustn't die. You mustn't trade yourself for a kill unless you have no stacks and your team is behind, or you're killing Cho Gall. Be prepared to back if anything goes wrong, you won't always kill but you shall never die. What you want here is an unfair 1v1 with a low HP unsuspecting opponent. You'll have to burst him down instantly because you're in his base and dangers are everywhere. Be quick or be dead.

1. Your target goes hearthing/drinking around the fort

Most people just go behind their fort to start hearthing or drink and wait a few seconds to let the healing kick in. If you can get there, just know if you have time to put your holo decoy first (see holo decoy section). If you don't go holo decoy first, you're basically all in (it sometimes work). Always wait for the holo decoy to hit the buildings before uncloaking yourself. The most important is to be out of reach of the fort or let the decoy get the aggro, if he hits you you'll probably die (slowed, uncloaked and under fire from at least 1 building is a bad situation for Nova). Sometimes you'll have to take that risk, but remember your #1 rule: don't die.
You'll get a lot of free kills around the fort, especially in QM. A lot of Abathurs (see Abathur section) and Murky eggs too (see Murky section).

2. Your target goes hearthing/drinking around the keep

You can't do much here if no building is down, not even enter. Sometimes a wall/door will be broken and you can get through, sometimes it's a door without turrets to the side of the base (like in Battlefield of Eternity), but most of the time you can't enter until the main door is down. It's a place that feels safe to the opponent so sometimes he will hearth just behind the turrets. An holo decoy for vision + an auto attack and a pinning shot (+ nuke if needed) can secure the kill. Remember your snipe won't get through.
If this area is open, the same rules applies as in forts area except that it's even more dangerous (less space, less distance to their respawn zone).

Nova's abilities

Trait: Cloaking

1. How does it work ?

After 3 seconds of not breaking it (see part 4 of this section) you'll cloak. You'll also uncloak under conditions (again, see part 4).

2. What is it good for ?

- You're hard to see on screen. And if you don't move you're even harder to see. At low levels (ranks 25 to 50 roughly) most people won't notice you at all even if you're moving next to them. At higher ranks lots of people will notice you, and some will spend their whole game trying to hunt you. People think that's all there is to cloaking and that's why they think Nova is just a gimmick hero. Good news, it's not.
- You don't show on the map at all while cloaked. It's the best advantage. You'll roam a lot, you'll scout a lot and you'll never show up on the minimap.
- Minions, bosses, mercs and buildings won't attack you which is convenient when chasing. And you'll chase a lot.
- Generally in bushes + cloak you're very very hard

3. What threatens it ?

- Peaking talents / traits are huge threats to you. Tassadar is the obvious threat as he can do it every 30 seconds, but some heroes can pick this talent. It's a good thing for you as it messes with their build, forcing them to drop very important talents. Karhazim (Kharazim's peak talent is very annoying as he auto casts it very often), Uther, Murky and Kael Thas can get the "clairvoyance" talent. And Brightwing has some sort of clairvoyance talent, except it's only used when she teleports so it's less effective in my opinion, but still a threat. Anyway, the revealed zone can be avoided as you can spot it on screen, unless you're already revealed by it.
- You can be spotted in any place the opponent has vision, even if they're not around, but they'll have to watch your location carefully. This includes enemy controlled watchtowers, Zagara's Creep, scouting drones (talent), minion waves, buildings, neutral "vision for all" spots like a tribute... don't let them spot you for free.
- Most heroes can reveal you with an area of effect attack. Anything that does damage without a need to target you will reveal you. Countless Novas/Zeratuls die to this. If you feel they can see you when you're cloaked, keep some distance because being revealed often means death. Valla, Sylvanas and Abathur's symbiote have one very good revealing abilities. Most healers have more trouble, but I don't think any hero lacks a AOE spell. Karhazim cannot reveal you at all with its abilities only. Lili cannot reveal you either. Sgt Morales will have trouble because her grenade explodes on visible enemies and you're not visible (I think it still automatically explodes at a certain range //test). Reghar cannot reveal you unless he uses his thunder shield on him or any enemy near you, so if you keep a little bit of distance he just cannot reveal you. The Lost Vikings can only reveal you with the spin talent.
- Your body is still here so sometimes other heroes will stumble upon you, and when they feel like they've knocked into some invisible obstacle, they'll understand quickly it's you. Flee!
- Enemy core is a threat to you because of its AOE auto attack may accidentally uncloak you but it doesn't reveal you anymore automatically.

4. Who / What can use cloak ?

Only 2 heroes in the game have cloaking traits: Zeratul and Nova. They'll spend most of the game cloaked, only revealed when using an ability, attacking, hearthing, mounting (you'll re-cloak after mounting, and un-mounting doesn't uncloak you), dancing, and losing HP. The same effects will prevent you from entering cloak, so damages over time like envenom are huge threats to you. And revealing traits / talents will prevent you to cloak for 4 seconds usually.
It has to be noted that a few more effects in the game involve cloaking:
- Nova's clones spawn cloaked (if she's cloaked) and they'll uncloak by hitting enemies or buildings (see holo decoy section).
- Raynor's banshees (one of his ultimates) are summoned cloaked but since they're here to attack they usually break it quickly.
- Tyrande's ultimate Shadowstalk cloaks her whole team for 8 seconds. Chances are most of them will be surprised by it and keep attacking or losing HP at this moment and break cloaking quickly.
- Murky has a level 13 talent that cloaks him for 5 seconds with a 20% speed boost when he exits his egg. Very interesting talent but it isn't a viable pick on this tier.
- Sylvanas can get a level 7 talent for cloaking 3 seconds after using her shadow wave. Useless talent.
- Abathur's hat on a cloaked hero can launch cloaked attacks without revealing the hero, which is kinda broken. A hatted Zeratul will be able to interrupt an objective a long time vs 3 heroes without taking the slightest risk, having one of the best escapes of the game. As a Nova, you shouldn't go close enough to enemies Abathur can hit it's spike burst, and he'll have trouble hitting with his needle. Worse, your holo decoys won't have a fake symbiote appear on their heads meaning everyone on the other team knows who's the real Nova.
- Other interesting effects involve Brightwing. She has sparkles appear over an hero when teleporting on him. I don't think these sparkles show if you're cloaked but it'd require a confirmation and I cannot test it. Also, it's reported that going from uncloaked to cloaked while Brightwing is channeling teleport on you can cancel it (more troublesome for Tyrande's shadowstalk BTW).

A general rule to cloaking / hiding is to hide where they won't even look. If your team is pushing their core, they'll focus their attention to the core and the people hitting it. If you're hiding next to the outer wall of the map they won't notice you and you'll have opportunities of kill on defenders. Whether you plan on playing Nova a lot or not, train to see the little light shimmer that shows an invisible thing (most likely an hero) is there. If you're good at it, you'll never fear Zeratul ever again.

Abilities

1. Snipe (Q)

Cooldown: 10 seconds
A huge damage skillshot with a pretty good range. It's the most damaging ability of your combo. It only hits 1 enemy so try to avoid minions, and even enemy walls. It's easy to miss since it doesn't have a big AOE. If you can get a good snipe on your target, you have better chances to make the kill.

2. Pinning Shot (W)

Cooldown: 12 seconds
A low damage slow with a poor range. It applies a 30% slow to the target during 2,25 seconds. If you don't get the level 16 talent crippling shot you won't have much use for it. It does slow the target, so if you have allies chasing him it may help while you mount, or it can give you time to mount and look for an opportunity. Slowing is always a good thing but you have to understand that if you used all your spells and 1 auto attack (and another after your combo), your next damage will be an auto attack per 2,5 seconds, and all other cooldowns will take 10 seconds minimum. So you can't do much on your own without it.

3. Holo Decoy (E)

Cooldown: 15 seconds
This ability is what takes your Nova play to another level. It has plenty of uses besides DPS. I used to hate it, now it's my favorite ability. Before you get Lethal Decoy at level 13 it does no damage. But it is still useful.
A. Holo decoy's instruction manual
Let's start by stating that your Holo Decoy follows some rules / patterns.
If you're cloaked it'll spawn cloaked. If you're uncloaked, it'll spawn visible. If it spawns cloaked people can notice it cloaked the same as they can spot you.
If he has a valid active target it'll: snipe > auto attack > pinning shot > auto attack (if he has time he'll auto attack again but after level 7 it doesn't). Sometimes he auto attacks before the snipe, sometimes not. But he always uses the snipe before the pinning shot.
Your decoy spawns with the same mana level as you, and uses mana for its abilities. So if you use it while being oom, it won't snipe and won't use pinning shot, only auto attacks. It has no DPS but the spells do work, meaning the pinning shot will slow the target, and the level 16 talent crippling shot will work too.
After level 13 it does 25% of your damage, be it auto attacks or abilities.
It's safe to say it prioritize heroes, but he may miss its snipe because of minions/structures or the target moving, and may not use his pinning shot because of its relatively short range. Be careful with the holo decoy, he's mana hungry, if you don't need to use it, just don't. One common mistake is to use it in your combo, and since it doesn't do damage until level 13 it's a waste of mana. You can use it for its pinning shot if you really need to slow your target (very rare).

Early game you'll want to use your holo decoy to test your opponents. Do they attack him as soon as he pops ? If they do that's a good thing for you, it means you will fool them a lot. Your holo decoy is expensive mana-wise so you don't want to waste it. Sometimes the opponent will waste more mana on it than it cost you, in this case you've won the mana trade. You'll want to help sieging (see D section below) too.
B. Baiting with holo decoy
You generally want to use your holo decoy to bait your opponents into wasting time / mana / cooldowns on it. I think there's 2 ways to make your opponents jump at it.
1. The realistic holo decoy
Don't throw your decoy just anywhere. Never throw it right next to another hero (Nova's ranged, remember?), and never throw it in the middle of something. You're Nova, you want to flank other heroes and then back in the shadows as soon as you've hit.
Make him look like a real Nova. Let's say you're in lane, cloaked. If you put your decoy in the bushes/smoke, just in range for it to hit an hero, it'll really look like a Nova trying to poke him. The decoy will look a lot more real as soon as you get your level 13 talent lethal decoy.
2. The "hey there, I'm a free kill" holo decoy
I love this one. You use the decoy in lane behind your enemy so that it's going to be hit by 1 turret anyway. It's a situation where the enemy has to very quickly decide if he's going for a free kill or just leave it because it's probably the decoy. They usually bite because a free kill on Nova isn't an offer you can decline.
It works also in teamfights. Make him look like he's flanking, but is still an easy target.
C. Helping your teammates with Holo Decoy
Remember: don't die, don't sacrifice for a teammate unless he has 20 doubloons on Blackhearts. Only help by staying safe. Helping/saving a teammate can only be 3 things with Nova's holo decoy (we'll talk about the nuke later). One is trying to make the worst and fragile bodyblock in the entire game (not recommended but in very rare occasions it works). One other is bursting down the chasing enemy. It doesn't happen very often somehow (usually when an ally is chased you're 2 levels behind, he has no life and no mana left and you're not so good either).
The last and best one is to use your holo decoy. It'll slow them (pinning shot), it'll show them that there's another opponent who can attack them and it'll give them a yummy target (remember, everyone hates you). Of course you may want to use your own pinning shot too but it's risky. Balance risk and reward. If your ally has to die, so be it. Don't lose your stacks, don't die for nothing, don't trade yourself.
D. Siege utility
Yup, you've got the worst laner in the game but you've got a real siege tool with holo decoy.
You can soak a lot of bullets from turrets by using your holo decoy in front of their gate. It'll soak easily 5 bullets from each turret, which is a lot. If you have nothing better to do it can really help your team early game.
Another siege utility is to go finish a distant fort. Now low health forts/keeps are shown on the map, which helps you even more. This is something you cannot do until level 13, unless the fort is really really low (less than 5% health maybe). Throw your decoy, let it get the aggro, then give your all on it and back even if it didn't die. Yay, free fort. It's up to you to decide whether you want to nuke it or not (see precision strike section).
As a side note, if you can use that strategy to snipe fountains when the walls are open, you're really helping your team.
E. Scouting with holo decoy
Holo decoy can be used on bushes/smoke to see if it's safe to step in. It's a huge mana waste but a life saver. Let's say the other team is maybe on boss on Pirate Bay. You have a very high chance they're just hiding in the smoke waiting to one shot the first hero who'll scout there. You being cloaked doesn't make you safe. They're all here and they're waiting for you. They'll spot you, and if you come too close you're dead. In this case throw a decoy in the smoke to get vision. If the decoy can hit an hero it's even better it may trick them into doing something stupid.

4. Precision Strike (R)

Cooldown: 60 seconds
What I love about precision strike is how much utility it packs. It is an AOE attack with global range, meaning you can cast it anywhere even if you're not there. It'll show where it'll hit just before striking so your opponents can dodge if they're fast (there's a 1,5 seconds delay), and then nuke the area. When the nuke lands it deals a nice but not-so-high damage to heroes hit.
Keep in mind that the small delay makes your nuke open to dodge but is in fact a strength. OK you'll miss a lot of nukes, but you'll be able to play some mind games with your opponents, because even if the damage isn't very high, your opponents will almost always try to avoid it, and you can use this.
Also remember that using the nuke uncloaks you, so make sure to not be caught off-guard while nuking somewhere else.
A. Global range thoughts
To me, global range abilities have a special flavor. You have to know at all times if there's a good place to nuke, so you'll have to develop a nice map awareness. Global range is the basis of precision strike's utility. In terms of raw mechanics the nuke can be used to zone out opponents or to hit opponents (details below). Global range = more demanding in terms of map awareness, but more rewarding.
B. Precision strike as damage in teamfight
Whether you're here or not, precision's strike most common use is teamfight, with 3 primary uses:
- try to hit stacked heroes
- zone out opponents, maybe to counter a dive, maybe to separate their frontline from their back, or other situations.
- combo with an ally. Your best combo partners are:
-- Zagara's Maw (the maw will squish 3 times, nuke at the third and you're guaranteed to hit all of them)
-- Zeratul's void prison, you need to time it right before it expires
-- Jaina's Ring of Frost will root enemies for 3 seconds so just nuke when they caught
-- ETC's Mosh Pit. If he caught at least 2 enemies, just nuke on ETC. No timing or skill required, you can't miss this one even if he uses the slide skill at level 20.
-- Gazlowe's Grav-O-Bomb 3000, after 2 seconds it'll pull the enemies to the middle, so if you feel it's going to catches enemies just wait 1 sec and nuke in the middle.
-- Leoric's Entomb. You have 4 seconds to place your nuke. If 2 or more opponents are stuck in this with Leoric hitting them, it'll hurt.
-- Not an ulti, but Johanna "Condemn" will pull the opponent's to her with a 1sec stun. When you see her using it (yellowish circle around her) you can nuke on her. She has a 1,5 delay while you have a 1 second. It's very effective if she grabs many enemies.
-- There are many other combos but they're more rare to pull. Like Cho's upheaval, it works well theoretically but you shall never play Nova with Cho Gall. Falstad, Valla, Tassadar, Uther, Butcher, and Murky have ulti that are semi effective combos with Nova (or very effective but hard to pull).

Don't use your nuke in teamfights right before the fight, even if the enemies are stacked and you can hit 5. They will retreat or their healer will do their job and you'll waste your nuke. Unless you pull a combo or try to zone them out, never use your nuke before or in the very beginning of the fight.
C. Save an ally
An ally's life is more important than a 60 secs cooldown nuke. So, if an ally is being chased and probably won't be able to escape, just nuke on him (with the delay it'll hit just behind him), it may zone out the chasing opponents. If they're many and full health they may be good enough to just step in the nuke and don't care, then you have just wasted it and your ally is dead, sorry. Most people will be scared though and it works more often then not.
And it can also simply unmount the pursuers, which can save your ally.
D. Destroy building
Finish that 2% health fort from the other side of the map. Just use it if you're 100% sure it'll die.
E. Defend a lane
For some reason you have to defend a lane versus 1 camp and 2 minion waves. You can kill them with your abilities and auto attacks, it'll take roughly 2 months, or you just nuke and move on. If no-one can come defend it for you (dead team, team pushing at the opposite of the map, allies who can't look at the map), just nuke.
F. Chase / finish opponent
My favorite use by far and the one which fails the most. 15 % HP Kael Thas is slowly retreating to its base ? Just nuke right before him. From the time he'll have noticed the nuke he'll step right in the middle of it making it too late to dodge. Often, he won't even notice and just die. Sometimes he'll have the reflexes to dodge by stepping back. Congratulations, you just wasted a nuke. Or did you ? Very often, zoning out this opponent is the thing to do. Let's say our favorite prey Kael Thas is retreating to the right and your allies/you are chasing him. Nuking is front of him will either kill him (good), make him step back (or step bottom/up) and die to your team (good). It's a win/win situation. Just make sure your nuke will block his path.

To conclude, just remember that it's always good to trade your nuke for a kill, for a lot of damage on enemies heroes, for a fort/keep or to save an ally's life.

5. Triple Tap

Cooldown: 100 seconds
Let's be clear, this ultimate ability isn't a bad one at all. It's just that precision strike is way better. Triple tap will make Nova visible, channeling 3 homing blows on an enemy hero. There's a blue laser that shows the blows's path so it can be dodged (with special abilities) or blocked by enemy heroes / structures. They deal a lot of damage, if all 3 hits connect you'll have twice the damage of precision strike on 1 hero. It has a very decent range, and will follow the enemy almost everywhere until it hits 3 times.
Pro's:
- very good at finishing a fleeing target.
- very good at clearing a team when you reach level 20, you can chain kills and dominate teamfights.
- very high damage if all 3 blows land.
- you'll get last hit kills with it, so that's more gathering power stacks for you.
Let's see the cons:
- it's channeling a long time, blows are delivered one after the other, and if your target is escaping it means a long channel
- you're uncloaked and immobile with a "free kill" sign on your forehead
- you can be interrupted by stuns
- triple tap's blows will follow the target but hit the first enemy hero / structure on their path. Meaning it's very easy to block for your opponent if they're half decent. Even a wall will block it.
- your target exiting / entering mines will cancel triple tap
- your target can dodge it with special abilities like Illidan's metamorphosis
- basically you burst a target, which you already do with your abilities
- level 20 of triple tap is awesome but has cons: rewind is better, bold of the storm is more useful, and if you don't kill your target -which will happen a lot- you lose its benefits.
- 100 seconds cooldown over a 60 seconds Precision Strike

Overall it's a bit too unsafe, it does what you really do well already, and who would pass on a global range ultimate ? (except ETC!)

Your combo

Your best combo would be:
Before level 13, perfect combo:
1 auto attack + 1 snipe (fast enough for Ambush Snipe to work) + Pinning shot + 1 auto attack at the end. Holo decoy can be timed when it's convenient, it deals no damage so I don't count it.

After level 13:
Holo decoy is usually the way to engage as it doesn't uncloak you, so you don't lose the benefit of your ambush snipe. And it may confuse people into attacking it which makes you safer, even better if they use any ability. The rest of the combo is the same.

After level 20:
I don't think it's possible to get 2 ambush snipes with rewind without wasting other abilities so let's forget about this. Use the same combo. Then rewind, then your 3 abilities again starting with holo decoy. You want to use the Holo Decoy first because 5 Novas melting your face is both confusing and deadly. You want your decoys to use all their spells.

To be honest, the ambush snipe being so powerful, it's OK if you engage with it then auto attack. You really don't want to miss the snipe or lose the ambush bonus.But if you can get 1 auto attack in the beginning and 1 in the end your combo is perfect, it's 3 seconds of lethal burst.

Build Order

Tier 1. Level 1

a. Ambush Snipe (pick)
Makes your burst even more dangerous. Your snipe will hit 20% harder when cloaked or uncloaked since 1 sec tops. Of course, if you miss lots of snipes you lose even more potential than with other talents. But if you can't snipe well go train and come later.
b. Psi Op Rangefinder (very bad)
The extra range is very situational meaning it'll come in handy once or twice per game. The reduced cooldown is not enough: when you finish your combo your target is either dead or you are, you don't have time to wait 8 seconds for your snipe's cooldown. You want your engagements to last 3 seconds tops, not 8 seconds.
c. Tazer rounds (very bad)
Your pinning shot is not very good so you may not want to waste time upgrading it. And you usually don't want to chase by walking 4 seconds behind the enemy, so I don't recommend it. The pinning shot slow is not for you, it's for your teammates, you don't chase by walking.
d. Conjurer's pursuit (bad)
You'll roam a lot so you could gather a lot of globes. And mana is Nova's first problem. But it's way less interesting than Ambush Snipe. I think it can work if you roam all the time and pay attention to the globes.

Tier 2. Level 4

a. Perfect Shot (very bad)
Mana refund on snipe is not useful. You'd be short in mana even if you had free mana snipes all game long. And this level tier has very good talents.
b. Remote delivery (very bad) Extra range on holo decoy is good in chasing situations but very situational (1 or 2 times per game). Lower cooldown on any of Nova's ability isn't really useful. Kill your target in 3 seconds of die/flee.
c. Gathering Power (pick)
You'll gain 2% ability damage bonus per kill, to a maximum of 30%, and lose all your stacks on death. By now you should know 2 things:
- Are you in a good day ?
- Is the other team able to hunt you:they have Nova counters and/or don't bite on holo decoys and/or can see you cloaked pretty well ?
If you feel you're going to die a lot, don't take this one. You lose all your stacks when you die. Also sometimes you'll do your job, contribute in lots of kills but don't have the last hit, like 2 kills 0 death 9 assists. You played very well but you only have 2 stacks, you're unlucky and that makes your talent pick not-so-good. It unfortunately happens a lot since the "kill/death/assist" patch.
d. Envenom (situational pick)
Envenom is always a good talent, and deals nice damage of time while uncloaking that Zeratul for 10 seconds. The range is bad but you can definitely use it in your combo. Gathering Power while not dying is always better though.

Tier 3. Level 7

a. Explosive round (very bad)
Area of effect damage on your snipe. This is wrong for so much reasons. You don't want to lane, you don't want to hit several heroes because Nova vs 2 or 3 = dead Nova. Definitely bad.
b. One in the Chamber (average)
Your auto attacks deal 180% damage after you use an ability. You'll actually deal more damage with this one than with Armored Shells but it's more complicated. Deal an ability, auto attack, ability, auto attack... It's more complicated to use as you'll have to alternate AA and abilities, and slower. But you'll have a slightly higher burst if you can AA 3 times with the 80% bonus. One in the Chamber is inferior if the fight gets longer than 3 auto attacks or if any of your abilities is on cooldown. If you can only put 1 AA for some reason (and it happen a lot), Armored Shells is always stronger.
One in the chamber: 180% AA * 2,5 (it's 2,5 times faster) = 450%
Armored Shells: 250% * 2 (it'll hit 2 times in 2,5 secs) = 500%
Let's look at combos:
One in the chamber: holo decoy + AA 180% + snipe + AA 180% + pinning shot + AA 180%
Armored Shells: AA 250% + Snipe + Holo Decoy + Pinning Shot + AA 250%
And now all your abilities have at least 5 to 10 seconds of CD, meaning the 80% bonus is lost until the abilities are off cooldown.
c. Armored Shells (pick)
Your auto attack deals 250% but is 250% slower meaning you hit less, but harder. Your DPS is 100% the same. What is it useful for then ? Your first auto attack will have the power of 2,5 AA, so it helps your burst. Also you can move freely while your attack "reloads" (there's an animation on your canon that helps you notice when it's ready again). Beware, if you right click a target and your AA is on CD, you'll just stop moving while your AA is on CD. And you never want to stop when chasing so be careful with this. When you get this talent is when you start being dangerous in lane. Moreover, you'll need to start hunting Abathur if you're not behind in levels.
d. Covert ops (very bad)
Extra slow with complicated stack rule. One of the most useless talents for Nova.

Tier 4. Level 10

a. Precision Strike
In 99% of the cases you'll want to get this one. See precision strike section for more details.
b. Triple Tap
Don't pick it unless you really love seeing blue beams. See triple tap section for more details.

Tier 5. Level 13

a. Lethal Decoy (pick)
Now your decoy deals damage! He'll look more and more like a real Nova so you may want to test your opponents again and see if they bite now. Also, it's more DPS for your combo and you want that. More safety + more DPS = win/win. It's by far my favorite Nova talent. There's nothing much to say than what was said in the Holo Decoy section. You can now use it as a long range ability to hit fleeing targets (your holo decoy range + his ability/AA range is very good).
If you pass on this one, don't pick the level 16 talent "Double Fake", and you may want to pass on rewind at level 20 too.

You don't want to pass on Lethal Decoy at all, you can't afford it. But let's say you want to try other talents just for fun:
b. Advanced cloaking (average)
Health regeneration isn't so useful, as you'll run out of mana before you'll want to heal. But to be honest it's nice to be full health all the time, even if it's kind of overkill. The speed bonus is very good because you'll be able to chase targets by walking. It's handy but if you mount efficiently (see chasing section) most of the time you won't need it.
c. Headshot (bad)
Lowering all abilities cooldown is great, but lowering it with kills is not good. If you make one kill, just back. Don't engage multiple targets or you'll die. It can work in teamfights but is overall not so good.
d. Spell Shield (bad)
Spell Shield will be very efficient when picking Jaina or Kael Thas but not so much versus Raynor/Valla/Falstad... You best way to be safe is to make sure your target dies within 3 seconds. You don't need a shield.

Tier 6. Level 16

a. Railgun (bad)
Snipe hits all in his path with reduced damage beyond the first target. The cooldown is reduced per target hit. This is clearly a lane talent, so it's not useful. You don't want to hit multiple targets, you want to kill the one in front of you.
b. Crippling Shot (pick build 1)
During the slow of pinning shot (2,25 secs if you didn't upgrade it) your target becomes vulnerable, with 25% increased damage. It's pretty nice for boss fights, and it works well in team fights. You should know by now if you need it in fights or if you want to stick with your hero hunting. If the other team is always moving in 5 man stacks, as it'll be often the case if you do your job well, you'll need to take Crippling Shot. Buffing pinning shot, which is a short range ability increases danger for you so consider that too. Double fake adds safety, crippling shot adds risk.
The vulnerability is quite short so you should use it on the target your allies focus to quickly burst him down, it's not an initiation tool unless you're very coordinated with your team which won't happen. Remember your holo decoy will apply the 25% vulnerability too! Just launch it next to your target so he focuses him.
c. Double Fake (pick build 2)
One fake is good, two is awesome. It adds more damage to your burst, and more safety for you. Just be sure to move before uncloaking as the second fake spawns on your location. Double fake on 1v1 is really awesome, even more at level 20 with rewind.
d. Overdrive (bad)
On activation this talent will give you an increased 25% ability damage during 5 seconds + but with a 40% mana cost increase. You won't have time to launch your abilities twice until level 20 (rewind) because of your long cooldowns but using all 3 (and the nuke) with this bonus is pretty nice. And with rewind it becomes insane damage. But you rarely will have enough mana to do so, and it's in fact less powerful than crippling shot which makes your target take 25% increased damage from all sources, including your auto attacks and your allies.

Tier 7. Level 20

a. Fast Reload (good)
Awesome talent, if you're good and your opponents are bad enough to let you do it, you may be able to chain kills. But you shouldn't pick this ultimate in the first place.
b. Precision barrage (good)
A second nuke for free! That's pretty good but the other 2 talents are more useful. You won't be nuking all the time in the first place so with this talent you'll underuse your nukes. And if you don't, it's even worse: I noticed having 2 nukes in store often leads you to waste it on not-so-important targets.
c. Rewind (build 2)
With Double Fake at 16, you really shouldn't take any other talent on this tier. With rewind, you not only barely double your burst damage, but you add 2 decoys to the mix, for a total of 4 ! All of them will hit the enemy and confuse him. Again, this talent is more safety + more damage.
d. Bolt of the Storm (build 1)
An escape! Yay! This talent allows you to play a lot more risky engagements while being able to escape very efficiently. Of course you can use it to chase if you're 100% sure you won't need it to escape right after. Rewind is better but greedier, as it makes you less safe than Bolt but adds damage.

Power spikes

Every talent on this build is a power up on your DPS, but these 4 power spikes make a difference.
At level 7, the anti armored shells help you burst your target more efficiently. You'll have to be uncloaked less time to deal the damage of 3 auto attacks, so you're safer and deadlier.
At level 10, the ultimate is of course quite powerful. It's a good combo with heroes like Jaina, ETC or Zagara, and it's packed with uses (see ultimates section).
At level 13, my favorite power spike of all, is when you get lethal decoy. It's a good boost of your DPS and it makes you safer as people will usually take the bait and attack the holo (since it deals damage). At level 13, if the game is not already desperate, is when you start to be very dangerous.
At level 20, with rewind (if you go Bolt of the Storm you still get a nice power spike). Trust me 5 Novas hitting you is both deadly and confusing. It actually helps you be safer while being deadlier.

If you get envenom at level 4, it is quite a good power spike, but it's not the best talent to pick if you can afford Gathering Power.

Drafting Nova

As a rule of thumb you should never draft Nova in the earliest picks (1,2,3 picks are forbidden), except if you know for sure they'll waste their efforts countering you. On Dragon Shire, and it may be the only map where you can, there are few big teamfights until late in the game, you can 1st pick Nova. They'll pick Tassadar ? He's on 1 of 3 lanes so just try to avoid his lane (or abuse the fact they'll think you'll avoid his lane by surprising him). Now they don't have the support they wanted, they have one they picked for you. It's a good thing for your team.
It's the same with any other Nova counter. They may even pick 5 counters but it'll give the rest of your team an edge, and they'll have to forfeit on some very important picks (mages, specialists and Tyrande are easy prey to Nova).

When to pick Nova is a combination of 3 factors, like every other heroes, but it's way more important with her:

1. The enemy team

The enemy team mustn't have too much hard to burst targets. Double warrior with Uther is a no-go. Tassadar is a real counter to cloaking so try to not pick Nova after he's picked by the opponent. You're easy to counter / lockdown with stuns and evenom so you may want to take this in consideration.

2. Your team

Your team must allow a ranged assassin who won't soak damage in fights at all and won't have sustained damage. And you have no waveclear/lane presence, no stuns and no escapes, take that in consideration. Nova + Cho Gall = bad lane presence for example.

3. The maps

There're 3 awesome maps for Nova: Blackheart's Bay, Dragon Shire and Tomb of the Spider Queen, and 1 awful map: Mines (RIP, I won't miss you). More on that on map section.

Heroes guide (with and versus you)

1. Warriors

With: Their main job is to soak damage and protect the backline and you're not in the backline most of the time. Rarely you'll meet good roaming warriors (ETC / Johanna / Leoric) who understand when you're about to pick an enemy and come help you. They'll make your life so much easier, but it's pretty rare. When you meet one, don't hesitate to ping everytime you're about to move on a new target.

Versus: Bad targets for burst unless they're already very low HP. They don't fear you and will try to reveal you / chase you while being safe from your burst. Too many warriors / tanky heroes on the opposite team will turn you into an useless hero.

2. Supports

With: you don't require much heal at all. You'll run out of mana before running out of life most of the time. So it makes a global healer less efficient, although it's not that impacting on the game. Lili, Malfurion and Tyrande healing ulti are less efficient since you don't need them. Karhazim and Brightwing area healing are a bit less powerful too because you usually won't be in the healed zone. Anyway that alone isn't so important to impact your pick.
Versus: you have to burst your target before any healing can kick. Uther's Divine Shied, Karhazim Divine Palm and Tassadar's shield are a pain. Also, lots of support have peaking talents (see Cloaking section) so you want to be careful on what support they pick. Tassadar (see Tassadar section) is the one you want to avoid the most.

3. High mobility heroes

With: Falstad, Brightwing, Illidan with the Hunt, ETC with Stage Dive (well, hope they never pick Stage Dive) or any other high mobility hero have a nice synergy with Nova. Ping your target, if they come it's a guaranteed kill.
Versus: For the same reason, they counter you well. If you burst fast enough Brightwing won't have time to save your target, but Illidan will kill you for sure.

4. Particular cases

Abathur
With: Symbiote doesn't work well on Nova. Abathur lacks early/mid game lane presence (except during objectives where he can double soak) and Nova has none, so you're basically forcing your 3 teammates to solo lane (on 3 lane maps).
Versus: you counter one another. He'll make your roaming hell with his mines, but you'll kill him if he's not in the keep zone of its base. After level 7 you'll want to go Abathur hunting around forts and in bushes (before level 7 your burst may be insufficient). Follow the lane where he spawns his locusts, but don't forget if you can see them he can spot you. Don't try to burst Abathur if they're a level ahead of you, he won't die from it and you'll be in trouble. You may want to nuke him if you have no other way to finish him. It's definitely not a waste to do so.
To kill him in his base, you'll need to find a spot where you can escape quickly, or hide long enough to cloak back. Use your holo decoy, wait for it to uncloak or you're dead, it's very important as it'll soak the building's aggro. Then use your combo on Abathur. If he requires one last auto attack to die and he hasn't moved (happens a lot), sometimes it's ok to stay to finish him. Otherwise flee as fast as possible, even if he's alive (it's ok, you kicked his ass, he'll tell his friends how you didn't even care to finish him, he'll feel miserable - not true at all). Mounting to flee is a risk as it'll put you 3 more seconds uncloaked, I recommend cloaking and walking carefully to a safer part of the map. Chances are 1 or 2 heroes are on their way to hunt you and you prefer to be walking and cloaked than mounted and uncloaked in enemy territory.
Cho Gall
With: Gall can't lane. You can't lane. You'll lose unless the other 2 heroes are very very efficient in lane. Efficient (as in: efficient versus 2 enemies) lane supports are very few, Tassadar and Malfurion maybe. You probably already lost the game in draft. It happened to me twice in HL, 1 victory and 1 defeat. Both low level but tight games.
Versus: not much to say, treat him like a warrior, but a very dangerous warrior. You don't want him to chase you or get near you.
Murky
With: you're squishy, he's squishy, it's just too much squishiness. Avoid him on your team at all cost.
Versus: you counter one another. Of course you're an egg hunter and you'll insta kill him with AA + snipe, but his Octograb combo, whether it's pufferfish build or Trace's build, or even bubble build will kill you. If not he'll chase you with slime and bubble, and you're also dead if you can't burst him before. Also, you really don't want to trade yourself here. Not at all.
Egg hunting is a lot like Abathur hunting, except that the egg is often in the jungle. Don't waste time egg hunting unless you think he took a risk. When Murky dies, try to spot from where he comes back, and evaluate if the egg is far or not (long respawn means egg behind core, short respawn means very close egg). If you can do that, go egg hunting if you have nothing better to do. Even then it's not guaranteed you'll kill the murlock. And never trade yourself for Murky or the egg. Most people don't understand that it's not good to trade yourself for a Murky + egg. You'll still lose the trade exp wise. Murky will be pissed for sure, but that's all. The good news is the harder Murky will push the easier you'll get him or his egg.
Zagara
With: the more creeps she spreads, the easier your job. She usually wins her lane while damaging the opponent so you may want to come often to finish this Valla / Sylvanas / Nazeebo or whoever lanes against her. Her ulti allows great combo, but make sure she doesn't Maw as you Nuke because she may counter your Nuke (you'll both aim at stacked enemies in fights so be careful). The safe bet is to wait for her to Maw, then combo. You'll love to play with Zagara. Versus: creep is a pain, it can help good opponents spot you. The hydralisk / mutalisk will chase you, she has poison and evenom so she's annoying. But you're a bigger threat to her than she is to you.
The Lost Vikings
With: not much to say, help him notice when he's about to get ganked or counter gank the opponent. He's not in fights and you're hiding, so good luck with that. Avoid this pick if possible.
Versus: you'll want to hunt Baleog (green Viking) and Erik (red Viking). Olaf is just too hard to kill, don't go unless he's low HP. Your big strength here is that a TLV player will look at the map all game and you don't show on the map so you can ambush him efficiently. Ideally you want another hero from your team to do the same, while the other 3 delay the other 4 enemies. If you can do that you'll really be efficient versus The Lost Vikings.
To summarize, your hard counters are:
- Illidan because of the Hunt and because you just can't get away from him. Oh, and he's harder to snipe than most heroes.
- Tassadar (see Tassadar section), Tyrael because of Judgment.
- Envenom talent counters you because it's 10 seconds without cloak + damage.
- Peaking talents.
- Tanky teams because you won't burst them down.

Your burst counters anything that is squishy and wanders alone (most specialists and most ranged assassins) / out of position, and your roaming counters any hero that needs to hide stuff or himself.

Maps guide

Good maps for Nova are maps where it's easy and useful to roam. The best 3 maps by far are Blackheart's Bay, Dragon Shire and Tomb of the Spider Queen. The worst map is Mines but it's out of map rotation. It seems Nova has a high winrate on Towers of Doom but I didn't experience a real success with her on that map.

a. Dragon Shire

The objective never moves and is at 3 places in the same time, and stay open for a while.
You'll want to roam a lot. Your people will have to split 1 good laner top or bot, 1 guy mid, and 2 on the other lane. You'll roam a lot, trying to secure kills and givie vision to your team. It's a map where small fights occur all the time around the top and bot altars. If there's a fight (even 1v1), there's an injured opponent. Be there for him.
Also you can use your cloak to block a temple, and if your opponent doesn't have AOE spells he won't uncloak you, being unable to get it. For example the Medic cannot uncloak you easily (her grenade is too inconvenient to use without a visible target). A few heroes will have trouble uncloaking you (Thrall comes to my mind). When the dragon pushes you just be around cloaked, waiting for an opportunity to kill. Sometimes throw a holo decoy behind their door to get a few seconds of vision. Sometimes you'll want to delay the opponent from summoning the dragon. You safe bet is to be on your side of the lane, and use your holo decoy. Everyone knows the bushes right next to the dragon are full of people wanting to gank/delay the dragon, so it's risky to stay there. Snipping can be useful because of your range, but don't trade yourself for a dragon delay. Most of the time they'll still get it and you'll still be dead. They won't refund your life if you traded it for a useless delay you know. Also, you can use your nuke to delay the dragon's summoning. I prefer by far wasting this than my life. Around top and bot altars, you'll want to avoid hiding in the bushes as everyone always assume someone is there. Ganking an opponent by blocking his escape route is better done by going through the lane, cloaked.

b. Tomb of the Spider Queen

The objective is laning and remit, and it stays open for a while.
Roam a lot. Be careful of the smoke mid, it's a danger to you. Most people will wait you there or attack it blindly. You want to avoid this. The objectives are better accessed from the sides. They don't expect you to come from the sides. You're useless at collecting gems from minions, but you'll save lots of gems from dying mates thanks to your cloak. Be careful as your opponents may expect you to do this. You also can get gems under the opponent's turrets while cloaked. No gem is worth your life, but collecting these and the 3 ones you get by killing heroes is very usefull.
You'll be able to interrupt people paying gems a lot. Your holo decoy is your best friend.
There are small entrances to the 1st layer of the bases (top and bot), you'll want to use these a lot to chase hurt heroes. They don't expect you to go through there and kill them behind their own fort.
Bottom lane is where Sylvanas will over commit and die a lot if you can pull a good snipe. Remember people have to actively collect gems so you know where they'll have to walk. They'll take risks, you can use that.
You don't have to scout the boss a lot, you'll usually know if they are. Same with their bruisers. And it's too dangerous to go there alone, you won't have a lot of kill opportunities. You can roam the bot camp for easy specialist kills.

c. Blackheart's Bay

The objective never moves and stay open for a while.
Very early you'll want to roam, not only between the top lanes, but to the bottom too. Bot is where the specialists will face themselves. They take much pride in winning the lane, so if the opponent over commits you're in for a free kill. At the beginning of the game you may want to put a holo decoy on the tower so that your team gets vision. You can't do much more. Be sure to help your team for the first chest, whether it's mid or bot. Just let them know where you go by pinging (alt+hold left click, then release on the right icon).
As soon as there's some money in game (50 secs in = first chest), you'll want to give vision to your team. This is the key to the game, and that's also why Zagara is so strong on this map. Since a lot of heroes will be roaming bot/mid around the objective, if you can get vision to your team you'll often get some kill opportunities. Go see if they take their siege camp and if you can gank them there. If a good opportunity shows ping for your team to come. Check the doubloons camp just up the siege giants. Go see the pirate, go see if you can get a kill bot. And have a look at the bot bruisers BTW, it's good for ganks. You're more efficient by roaming in the opponent's side of the map. Usually you cannot gank them on their bruiser camp, your mates will be too far. If help is needed mid and top you can go, but you'll spend a lot of time in the bottom left part of the map.
Most people assume it is Nova's job to provide vision on the boss. I disagree here, if you give your team enough vision on the map you'll just know when they are on the boss. You usually won't have time to go there to check by yourself but anyway you're either already tracking 2 or 3 opponents, or they are bruisers, or they are boss. When your team wants to pay doubloons, you give them vision while not being too obvious and not in the path of the opponents because you don't want to be uncloaked by Tyrande's owl or Thrall sundering. Don't move too much when they arrive and try to get a kill when possible. (//schema?) If their team is paying you'll want to flank them from bot. If they're not committing to fighting your team and you engage them, you'll die. Wait for the fight or pick one only if they aren't grouped yet. You can delay them paying on the pirate with holo decoy or nuke. You mustn't use the smoke around the pirate much, because it's the first spot everyone checks or sends AOE spells to and you don't need it.

Ok now, how to improve ?

You have 5 big things to improve:
- your combo, by practicing it and making sure you hit all your abilities and 1 auto attack minimum each time. If you see any ability available after your combo it means that you failed to use it. Pay attention to your auto attack as you won't know if you didn't use it.
- your snipe accuracy, and this is done by practicing and focusing.
- your map awareness, and this is done by following this guide's principles: roam, always know what your opponents are doing, always look for a kill opportunity or a nuke opportunity on the map.
- your mind games with holo decoy and precision strike, and this is done by practicing and observing opponent reactions to these 2 abilities. Experience is everything here.
- your survivability. You should consider 90% of your deaths like faults from you. Why did you die ? How can you prevent this next time ? Watch the replay and analyze every death.

It is up to you to work these and improve your play. And most of all, have fun playing this great game.