Voidrotten Devourer

Voidrotten Devourer costs {b} less to cast for each Nightmare or Horror you cotrol, and it is all other creature types on the battlefield and graveyard.
Nightmares and Horrors you control have
"{t}: Add {b} to your mana pool or deal 1 damage
to target player and gain 1 life."
Deathtouch, Trample