Creature — Spirit
* / *+1
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.
Cards with the ability word "fathomless descent" have abilities that care how many permanent cards are in your graveyard.