Champion Concept: Delayed stat boost
I only have a passive idea but basically instead of the Champion's stats going up with level they go up every 5-10 mins when the Champion visits to fountain. And if they don't get it at interval one then they have two boosts at interval 2, and so on. The reward is that instead of stats that are about equal to other champs the Champion gets like 1.125-1.25x the stats other champs would have. At interval 4 they would max out at like 1.5-2x the stats of other champs. They would have an insanely weak early game but a VERY powerful late game.