Lord Xanathar

When Lord Xanathar enters the battlefield, target opponent reveals their hand. You choose a nonland
card from it. That player discards that card.

{b}{u}, {t}: Gain control of target creature with converted mana cost less than or equal to the number
of cards in your hand. This effect lasts until Lord Xanathar leaves the battlefield.
Whenever you draw a card, you may pay {1}. If you
do, target opponent puts the top card of their library
into their graveyard.