Hangry Wiitigo

Bloodthirst 5 (If an opponent was dealt damage this turn, this permanent enters the battlefield with five +1/+1 counters on it.)
Whenever a spell is cast, if its converted mana cost is equal to Hangry Wiitigo's power, counter it, then put a -1/-1 counter on Hangry Wiitigo.
Devolve (Whenever a creature enters the battlefield, if its power or toughness is less than this creature's, put a -1/-1 counter on this.)