Xenomee, the Nihilist

Flash
When Xenomee enters the battlefield, X other
creatures on the battlefield get chosen at random
from among all creatures on the battlefield. The
owners of the chosen creatures sacrifice the
creatures. For every creature you sacrificed this
way, put two +1/+1 counters on Xenomee. For
each creature your opponents sacrificed this way,
all creatures get -1/-1 until end of turn.