Rengar is broken because Ryan Choi said so.

4 Dorans because it wins games, if you don't have 4 of them, you automatically lose as rengar.

Pros: one shot anyone alone with your super awesome ultimate that gives vision on everyone because rengar is a hacker.

Cons: Stay away from team fights because this cat is scared of groups of people and only likes playing with 1 person

Kill lane, gank other lanes with ulti, get fed, win game.

Don't forget to use bush to your advantage. Hide in bush to farm and to intimate the enemy when you jump at them and show how broken I MEAN how strong your damage is. Try to ask for ganks against scary top laners like Jax and Darius.