Riot, Rengar REALLY doesn't have any counterplay.
He doesn't. If he has the stats to kill you, you're dead. Instantly. I'm speaking from the point of a view of an immobile mage in the midst of my team with Zhonya's Hourglass. I can't move my finger to the button before I'm dead.
Edit: Before I get all these posts from people telling me how bad of a player I am, please look me up first. I'm not horrible. Perhaps I'm not getting through to you because it's just text, but in game, I AM blowing up in less than 0.5 seconds. I am a Platinum player. And no, I'm not fifty levels behind. I didn't even lane against him. Rengar has minimal, if any, counterplay when he's sufficiently ahead, and that's as direct as I can put it.
(and these are the items everyone should have, if we are going role specific then
)
ya scrub