Shipbreaker Serpent

Emerge {4}{b}{g} (You may cast this spell by sacrificing a creature and paying the emerge cost
reduced by that creature's mana value.)
When Shipbreaker Serpent enters the battlefield, target creature gets -2/-2 until end of turn. If
there are three or more creature cards in your graveyard, that creature gets -4/-4 until end of
turn instead.