Karridyr, Cryonic Arcanist

Flash
When Karridyr, Cryonic Arcanist enters the battlefield, you may exile another target spell.
If you do, that spell's controller may cast it
from exile at the beginning of the next end
step without paying its mana cost.
The first archmage of Thoughtcastle to awaken
from slumber, he is not to be trifled with.