Golgari Gravegolem

({t}: Add {g} to your mana pool)
{3}, {t}, Discard a card: Add {b}{b} to your mana pool, then put a +1/+1 counter on Golgari Gravegolem. Golgari Gravegolem becomes a swamp in addition to its other land types.
Golgari Gravegolem can't attack or block unless there are four or more creature cards in your graveyard.