What happens if a player uses a card not in their registered deck list during a game?

When a player uses a card that is not in their registered deck list during a game, it constitutes a rules violation. Each player is required to register a specific deck list for a tournament, and playing a card that is not listed breaks this agreement. The integrity of the tournament depends on players adhering to their registered decks, as this ensures a fair and consistent environment for all participants.

Using a card that is not part of the registered deck list can lead to various penalties under the Magic Tournament Rules. Depending on the specific circumstances and the established tournament guidelines, consequences may range from a warning to a more serious penalty, especially if it is deemed intentional or if it affects the game's outcome. The premise is built around ensuring fairness and maintaining the structure of competitive play, so all participants have the same expectations regarding their decks.