Rengar is gonna/needs to be nerfed.
Earning those 5 stacks for his passive is too easy and with the right build, infernal drakes and elder dragon NightBlue3 was able to hit 1020 AD. With infinity edge and a guaranteed crit on rengar's leap with ult he is bound to do close to 2.5k ad not counting for armour or anything else that negates damage. NB did 1630 ad to a fizz by simply ulting and hitting him. I love Rengar with all my heart and enjoy the fact that they are changing up his mechanics and playstyle after so long but at the same time this is bound to be nerfed and it should because that is insanely unbalanced. I feel that a nerf to the passive would be a good way to balance this issue. By reducing the ad gained or by making it harder to achieve the stack.