Mana Thwart

Mana Thwart is blue.
Flash (You may cast this spell any time you could
cast an instant.)
When Mana Thwart enters the battlefield, exile
target noncreature spell.
When Mana Thwart leaves the battlefield, the
exiled card's owner may cast that card without
paying its mana cost.
At the beginning of your upkeep, pay {u}{u} or sacrifice Mana Thwart.