Devil's Die

When Devil's Die enters the battlefield, you lose
6 life, and target opponent gains control of it.
At the beginning your upkeep, choose a number greater than 0, then reveal the top card of your library. If its converted mana cost is the number you chose, you lose the game. If not, Devil's Die deals X damage to you, where X is the chosen number.
Discard your hand: Target player gains control of Devil's Die.