March of the Luna Deus

Search your library for a card, exile it face down, then shuffle your library. You may look at and cast that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell. If you do, target opponent gains life equal to the converted mana cost of the card cast this way.
"They thought us to be vanquished, exterminated, reduced to oblivion. They thought
wrong."