New hero: Cannibal that eats killed allies … and grows
How about a hero that cannibalizes their killed off allies to grow even bigger?
It could be a hero with weak attack (to start), but fairly decent health/defense. As its allies get killed off, it consumes them and grows bigger … if it is the last hero standing, it might grow to Titan size/power!
Strategically, this would force players to try to kill it first in order to not allow it to grow to big and be come uncontrollable.