Ravenous Grub

Hatch {g}. (Whenever you put this card from your
library into the graveyard, you may pay {g}. If you
do, then put this creature from the graveyard onto the battlefield.)
At the beginning of your upkeep, sacrifice a
creature or put the top card of your library into
your graveyard.
Ravenous Grub cannot attack or block unless a creature has been placed into the graveyard
this turn.