Challenge

Challenge
Keyword Action
Introduced	Mystery Booster
Last used	Mystery Booster
Reminder Text	No official reminder text
Scryfall Statistics
cards

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.

Such mechanics have been utilized in other card games for decades (most notably Cheat, and more recently Coup), Richard Garfield attempted to port the Challenge mechanic into Magic for Dominaria.

Rulings

From the Release Notes for Mystery Booster (August 18, 2021)

• 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.

Example

Example

Xyru Specter
Creature — Specter
2/2
Whenever Xyru Specter deals damage to an opponent, that player discards a card unless they challenge you. If challenged, and you show them two black cards in your hand, they must discard two cards.