Thief of Sanity 2.0

Flying
Whenever Thief of Sanity 2.0 attacks, look
at the top three cards of that player's library, exile one of them face down, then
put the rest into their graveyard. 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.