Exile the top three cards of your library in a face-down pile, then exile the top three cards of your library in another face-down pile. Look at the cards in each pile, then turn a pile of your choice face up. An opponent chooses one of those piles. Put that pile into your hand and the other into your graveyard. You lose 3 life.
If you have fewer than six cards in your library, the second pile will be smaller than the first. If you have fewer than four cards in your library, only the first pile will have cards in it at all, and the second pile will be empty. You may choose to turn the empty pile face up, but your opponent will probably choose to give you the empty pile regardless, unless they're feeling especially generous.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.