Gnarl-Petal Gorger

Whenever a creature card is put into a graveyard from a library, put a +1/+1 counter on Gnarl-Petal Gorger.
{1}{b/g}{b/g},{t}: Return a creature card with converted mana cost X or less from your graveyard to the battlefield, where X is the number of +1/+1 counters on Gnarl-Petal Gorger.