Lost, +Soul (2)
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
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.
Gatherer works better in the Companion app!