Jarvikyl, the Gray Mourner

Menace
When Jarvikyl, the Gray Mourner enters the
battlefield, you may have each player sacrifice a
creature.
Whenever one or more creatures are sacrificed,
you may have Jarvikyl fight up to one target
creature you don't control. If you do, Jarvikyl
gets +1/+1 until end of turn for each creature
that was sacrificed.