Avatar of Cthulhu

Avatar of Cthulhu enters the battlefield with a
-1/-1 counter on it.
when you cast Avatar of Cthulhu, you may
sacrifice any number of permanents. for each permanent sacrificed this way, put a +1/+1
counter on Avatar of Cthulhu.
at the beginning of your upkeep, each player sacrifices X permanents, where X is this
creature's power.