Ooh ooh oooooh! I love listing champion's abilities! It's really fun!
Karma:
-unconditional 525 auto attack range
-spammable abilities
-a slow with varying levels of power
-aoe damage at range
-two forms for each ability
-partial damage healing+2.5 second long root
-team wide shield
-boosts MS
-passive reduces ultimate cooldown
-has ultimate at level 1
-has a root that will still affect you through in-vulnerabilities (Such as zhonyas)
-reveals enemies affected by W
Wow!
All jokes aside, listing a champion's abilities is not an argument. Of course a champion's kit is going to sound really OP when all you do is list its strengths. We cannot say that something is overpowered in a vacuum, we need a point of reference to compare champions to.
Your comment is especially disingenuous when you take a second to think about Rengar's kit. His passive makes it so that, like Karma, every one of his non-ultimate abilities has additional affects to it. Realistically you are only going to be able to empower one of his abilities at a time. He is not going to have
-
A root
-
full damage healing within 4 seconds and a cleanse
-
AA reset (assuming you're referring to the one on his Q, I am regrettably unfamiliar with how rengar works now)
all at once in a fight. Assuming he is able to get all of his passive stacks that he needs in a fight, he is going to be forced to choose between one of those three options.