Full Build (IN THIS ORDER)
Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Why this build? (AD one)
When playing AD Rengar your job is getting single target picks, and doing it fast. With this build you will get the most single target burst out of any build, and do it fast. In the late game you can switch out the RFC for Shiv, but for early game RGC provides more burst.
Why this build? (AP one)
As AP Rengar your job is to jump on multiple people in teamfights and get two Battle Roars off. This significantly lower EVERYONE'S HP which is the reason why AP Rengar is underrated.