Ivara, The Infiltrator

Reach, Skulk
At the beginning of your upkeep, You may pay {u}{b}. If you do, target player reveals their hand.
You choose a nonland card from it and exile it.
Until end of turn, you may cast that it at any
time you could cast an instant. You may use
mana as though it were mana of any color to cast
it. If you don't cast it, return it to the bottom of
its owners library and the beginning of the end
step.