Daniel J. D'arby

When Daniel J. D'arby deals combat damage
to a player, you may pay {3}{u}{b}{r} and shuffle your library. Then, As many times as you choose, you may exile the top card of your library. If the total mana value of the cards exiled this way is 20 or less, you may cast any number of spells from among those cards without paying their mana costs.
If it is 21 you win the game.
If it is more than 21 you lose the game.