Souls of the Lost 
Creature — Spirit
As an additional cost to cast this spell, discard a card or sacrifice a permanent. Fathomless descent — Souls of the Lost's power is equal to the number of permanent cards in your graveyard and its toughness is equal to that number plus 1.
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL