Unending Plain

{t}: Place target nontoken creature you control
face-down under Unending Plain.
Sacrifice all creatures under Unending Plain, {t}: Gain X white mana where X is equal
to the toughness of the sacrificed creatures.
All sacrificed creatures may be cast from the graveyard until end of turn for {1} less.
Any sacrificed creatures which were not cast
by the end of turn, are instead exiled.