Mundo Ultimate skin concept. Dr Mundo and Mr Hide.
Basically the skin makes Mundo a small unassuming man out of combat, and when in combat he hulks out into a far more horrifying creature than current Mundo. As the game goes on, he begins to perfect his syrum allowing the player to choose custom parts for in combat mode, such as wings, a tail, ending with various 'perfect modes'. Im thinking giant brute, hulking monster, incubus, and just the young man again. I honestly think it would be a great idea fitting with his theme.