A Champion that gradually ages as the game gets longer
Preferably a mage...a cursed mage. Starts off young, as the game progresses, 1 or 2 ability changes/upgrades, they get stronger...they peak at a certain point in the game..like the 40-45 minute mark AND THEN, the champion gradually gets weaker the longer the game goes on.
It'll be a fun twist on things. The pick can be both good and risky all depending on how fast your team closes out the game.