Summon the End

Summon the End resolves in {x} upkeeps after it is played. When Summon the End is resolved, exile it.
For the duration it's in play, Summon the End reduces the mana cost of all Eldrazi spells by {4} (but no less than {1}) and gives them all Flash.
When Summon the End is resolved, each Eldrazi creature put into play using the effects of Summon the End must be sacrificed.