Ashioks Nightmare

Cant be countered, Hexproof.
At the beginning of each players upkeep that player Exiles a creature they control. Ashioks Nightmares owner may cast Creatures exiled by Ashioks Nightmare and may spend mana as if it were any type to cast those creatures.
Ive been searching for the perfect world, turns out Ill have to make it myself. -Ashiok