Form Shredder

Devolve (Whenever a creature enters the battlefield under your control, if that creature has less power or toughness than this creature, put a -1/-1 counter on this creature.)
Creatures that share a creature type with Form Shredder get +1/+1.
At the beginning of each upkeep, for each -1/-1 counter on this creature, it becomes the creature type of your choice until end of turn.