Seclusion Mage

When Seclusion Mage enters the battlefield,
exile target creature an opponent controls until
Seclusion Mage leaves the battlefield.
Spellcast - At the beginning of your end step, if
you've cast an instant or sorcery spell this turn,
you may cast creatures exiled with Seclusion
Mage, and you may spend mana as though it
were mana of any type to cast them.