Xila, Nightmarish Evolution

Emerge {3}{b}{g} (You may cast this spell by sacrificing a creature and paying the emerge cost
reduced by that creature's mana value.)
When Xila enters the battlefield, if its emerge
cost was paid, put +1/+1 counters on Xila equal
to the sacrificed creature's power.
As long as there are three or more creature cards
in your graveyard, Xila has trample.