Rot Fiend

Rot Fiend costs {1} Less to cast for each card in your graveyard
Rot Fiends power is equal to the number of creature types among cards in all graveyards.
{2}{b}{b}: Return Rot Fiend to the battlefield from the graveyard. Exile your graveyard, then put the top 7 cards from the top of your library into your graveyard.