Challenge

Challenge is a keyword action, introduced on a test card in the Mystery Booster set. A player may challenge another player to reveal certain cards in their hand to counter a certain effect. If the challenge is successfully met, the effect will be enlarged. If not, the effect is nullified.

If you're challenged, you may reveal any number of cards from your hand. The effect that allowed a player to challenge you will specify what you must reveal to win the challenge.

The Challenge mechanic was originally designed by Richard Garfield for Dominaria.