Festering Ghoultree

Decay (At the beginning of your upkeep, put a -1/-1 counter on this creature.)
{t}, Sacrifice Festering Ghoultree: Add
{b}{b}{b} to your mana pool.
Scavenge {5}{b/g}{b/g}{b/g} ({5}{b/g}{b/g}{b/g}, Exile this card
from your graveyard: Put a number of +1/+1 counters equal to this card's power on target creature. Scavenge only as a sorcery.)