I played a game of AP Rengar and he did a lot of dmg I got first blood but after a while I suddenly stopped doing dmg I did almost nothing and I kept dying.
I was aganist wukong top I built Deathcap and Abbyssal Scepter and he built black cleaver
Your best bet on building AP Rengar is... Don't.
Rengar is an Attack Damage scaling champion. His damage abilities both scale off of AD and only his Roar scales off of AP, which leaves you extremely weak when you are building for those items. Not only that, but AP items are not optimized for the stats that you are looking to build. You want cooldown reduction, attack damage, and the hydra so that you can reset your auto-attacks/burst down the other team as quickly as possible. As Rengar, you are an assassin. If you are not building yourself to do as much damage as possible, you are crippling your team.
You fell off because you only have one damage ability, your W. once your W is maxed, even if you use a double W combo, your damage will fall off hard because of poor scaling.
It's a troll build and was only good before his rework, not anymore.
