Tides Devourer

Islandwalk, hexproof
Devour 2 (As this object enters the battlefield, you
may sacrifice any number of creatures. This permanent enters the battlefield with two +1/+1 counters on it for
each creature sacrificed this way.)
At your upkeep this card must devours another creature, if you don't: tap Tides Devourer and sacrifice an Island.