Medivh's Poly Bomb is actually pretty nuts when used right.
Polymorph an enemy Hero, suppressing their attacks and Silencing them for 2 seconds. On expiration, Poly Bomb spreads to other nearby enemy Heroes.
The gimmick with it is that the spread can occur infinitely, as long as your enemy stays clumped together. Used right, this can be such an amusing and effective CC.
The closest thing we have to this right now is Varus' ultimate, but his is a root effect and is a skillshot rather than direct-target, plus it can't spread infinitely. The fact that Poly Bomb doesn't root you in place or even slow you means your team can mitigate/end its effects by spreading out. Used on a solo target, it isn't that strong.
If we got a new Champion with an ability that was basically Poly Bomb (Varus doesn't count), would it be totally busted?