Necrotic Wurm

Menace
When Necrotic Wurm enters the battlefield, if
you cast it from your hand, sacrifice it unless
another creature died while under your control
this turn.
Whenever another creature dies, if Necrotic
Wurm is in your graveyard, you may return it to
your hand. Otherwise, put a +1/+1 counter on Necrotic Wurm.