Love this build, but just a slight modification on your build and an endorsement on how good the idea revolving decoy build actually is

1st: envenom - at lv 20 it does about ~1000 dmg extra and a relatively short CD (60 sec) comparing to the frequency of team fights. Basically 100% guarantees a kill whenever u pop out against any assassins and specialists. Further secures a kill against any support at full health and guarantee a kill at 3/4 hp or 4/5 hp. And you don't have to worry about getting killed and lose gathering power's bonus. Just be brave and fight for your team's benefit.

2nd: DO NOT USE TRIPLE TAP. I'd highly recommend Precision Strike for most situations because now you can combo this skill with many of your teammate's ultimate skills, such as Zagara's R1, Gaz's R2, and Zeratual's R2. This also sync well later with double clone and rewind. I find triple tap heavily limited among experienced players except trying to catch Zeratual. Heck, triple tap doesn't even kill an experienced enemy Nova if she knows how to hide behind her clone, especially if she also using this build (double clone)

However, if your enemy team has Zeratual and depends on the urge of eliminating this threat... triple tap is better skill instead to counter his worm hole skill

3rd: lethal decoy + double fake
I'm not sure if people appreciate how crazy this build can be with rewind. I find myself taking down even wounded tanks (3/4 hp - 2/3 hp) with this combo at equal level.

1 Q + 1W + envenom + 1 basic + double lethal clone is already at least 3k dmg. (nope you don't get that w/ gathering power). Now if you use rewind immediately after this you get another 1 Q + 1W and 2 more lethal clone. Bear in mind that each lethal clone shoots a 25% dmg Q and a 25% dmg W, and a 25% dmg anti-armor shot. 4 lethal clones total to a full dmg Q, full dmg W, and a full dmg anti-armor shot. So with a rewind you get a total of 3 Q, 3 W, and 3 anti-armor shot all in about 2 seconds, and a Precision Strike to finish things off.

Also keep in mind that the slowing effect now prolongs to... probably at least 4 second because of all these clones shooting W. If in team fight that's probably 2-3 targets slowed. That sets you up pretty well for precision strike and for your teammates ultimate given how slow your target(s) becomes. And since precision strike is instant cast, you can just throw all your combos out and walk away. (using triple tab obviously tell the enemy which one is the true Nova among the clones...)

And the most important part: 5 Nova at once! That confuses the heck out of your target(s) and you'll most likely walk away alive. In addition all these basic atks from clone also removes most (if not all) block charges stored by skills before you land your own basic atk. I've even dared to 1 vs 2 now once I hit lv 20 because now I have a fairly large chance of surviving after killing my target. Double fake also helps blocking triple tap from enemy Nova.

So your ultimate combo at lv 20 is (in recommended order)

E + Q + W + envenom + basic atk -> rewind -> Q + E + W + basic atk + precision strike

How much dmg is this full combo? Well it depends on clone's AI and your position. At lv 20, conservatively speaking, it's probably at least 6k damage if some clones didnt fire. On average (based on my experience), it's about 6.5k dmg including precision strike. Max damage output is 6854 at lv 20 (source: talent calculator of this website).

Now that also changes Nova's strategy in team fight. You don't have to be a finisher. Be an initiator. That damage gives a fairly large chance of 1 enemy kill at the beginning of team fight, or severely damage 2 enemies. Gives you a great advantage for your team. And due to the instant cast of precision strike, you've a large chance of using all your skills before death (ppl like to target you when you use Nova... and Triple Tap can be easily interrupted)

And finally, if you want to die, die with everything in CD. Because the revive time is at least 60 sec in lv 20, when you revive, you can do everything all over again and cause a huge trouble for your team. You won't lose any damage output either as you would with gathering power. Just yesterday using this build, I was able to kill 4 wounded enemies alone (Valla, Illidand, Sitches, and Tassadar) when they were distracted by the Golumn boss in the Ghost Mine and my teammates were all dead (has video to show if need be).

Hail Nova!

From: Cutepenguin. KR server. About 55% win rate as Nova in 300 games. Started playing in Jan 2015 after the nerf. Longest winning streak as Nova in Quick Match: 9 games.