Summon the Lost

Summon the Lost resolves in {x} upkeeps after it is played. When Summon the Lost is resolved, exile it.
For the duration it's in play, Summon the Lost allows its controller to cast creatures from any graveyard and from exile. Each creature cast this way gains Haste and costs {2} less to cast.
When Summon the Lost is resolved, each creature put into play using the effects of Summon the Lost must be sacrificed.