Riot thinks rengar is one of the most toxic things in the league of legends right now.
I have 2 suggestions that i think would make balancing rengar much easier for them:
1) make rengars brush-jump mechanic exclusive to his Q instead of making it on every single auto attack. this would give him much less absurd harass and mobility in the early game on top lane, which is where his brush jump is most abusive. it would also still allow him to leap on targets from stealth by activating his Q.
2) remove empowered ferocity effects. being able to cast an ability twice in a row with no cooldown is an already absurdly powerful mechanic. he doesn't need extra powerful effects added on top of that. rengar does not need an extra powerful Q, he does not need a heal, and worst of all, he does not need a SNARE on his e-bola. his ranged snare is even worse than his no-cooldown brush jump in terms of its toxicity, and it's the main reason why it's referred to as e-bola. it gives people ebola.