So basically this is not that great. This is not some hidden op gem and I would not recommend turning this into a main, or playing this in really important games or where the opponent got a really strong comp. That said this is a really fun build that can do some crazy burst as well as annoy melee opponents in lane.

People will not expect the burst you can do with just an e and a couple aa early and late game your ult can out damage a Veigar's. Your W range is huge which can surprise an opponent who overstayed on low hp. Your W's cd is reset if you get a kill or if you detonate a max stacks E. This allows you to jump in for a kill and jump out. Also allows to double dip on the W damage if the opponent lets you E > 3 aa > W > aa > W. The burst from this is massive. If you are low and can bait an opponent into diving tower your ult can deal a massive chunk of damage and knock them away from you and deeper under tower, often turning a losing fight into a free kill. The damage of your E is not front loaded, so an opponent will often overstay in an engagement thinking they have more hp than they actually do.

It is best to play this against a melee/short range champ champ that does not have a strong gap closer. Try to save last hitting until they come close to last hit a minion then last hit your own minion. Each explosion will give you free poke at the enemy that does not aggro minions. Most opponents won't play around this very well since usually those explosions would deal negligible damage.

E > as many aa as you can safely get.
If you know you will be able to get 2-3 aa do a Q after E, this will turn those 2-3 aa into 4 aa.

If you want to turn this into an all in instead of a poke: after your E and getting 3 aa, W onto the enemy, pop E, W on them again, ult. If possible W slightly ahead of them so if your ult does not kill it knocks them away from their preferred escape path.

I am not sure if this is a bug or something I am not understanding about the mechanic, but sometimes, your E's passive part will not proc. It is very rare and I am trying to pinpoint exactly when it happens, but it does make this a little weaker.

I am adding match-ups as I encounter them a couple of times. As a rule of thumb anyone with a strong shield or really long range is gonna be a problem.