A Boss Duel (ボスデュエル Bosu Dyueru) is a special type of Duel performed in Japan during a Yu-Gi-Oh! Day event. During these Duels, a shop staff member uses a Boss Deck and up to 3 players can challenge that Deck at once. Each Boss Deck is designed as a mock-up of a villain from the anime, with each card based on either an extremely powerful anime-only card or the anime counterpart of a physically existing card.
- Each player starts with 8000 Life Points. The boss starts with 8000 Life Points × the number of challengers.
- The turn order is Boss → Player A → Player B → Player C → Boss
- Fields are not shared. Each player can have up to 5 monsters.
- Players on the challenging team can talk with each other and show each other their cards.
- Face-down cards controlled by a challenger can be used by any player of the team.
- If a player on the challenging team achieves an alternate victory condition, they inflict 8000 damage to the boss instead.
- If a player on the challenging team loses, that player sends all cards from their field to their Graveyard.
- Before starting Player A's turn, the team can choose to activate 1 of the following effects. Each of these effects can only be used once per Duel:
- During the Battle Phase of this turn, double the ATK of all monsters of that team.
- Instead of conducting their normal draw during their respective turns, the turn player (except the boss) adds 1 card from their Deck to their hand.
- Choose 1 player. That player gains 4000 Life Points. (If you choose a player with 0 Life Points, that player returns to the Duel.)
- The boss only has 8 cards in their Boss Deck/Main Deck, and no Extra Deck. Five of these cards are marked "Start" (初) in the place the Attribute circle would normally appear, while one each of the other cards is marked "1", "2", and "3".
- The boss's starting hand contains the five cards marked "Start", and the remaining three cards are placed in order (with the card marked "1" at the top of the Deck). The Deck is not shuffled at the start of the Duel.
- The boss cannot lose the Duel due to being unable to draw.
- During the boss's Draw Phase, after conducting their normal draw, the boss adds all cards from their Graveyard to their hand.
- Cards owned by the boss cannot be banished. If a card the boss owns would be banished, it is destroyed instead.
- The boss can Normal Summon any number of times.
- Cards owned by the boss do not have Levels/Ranks, Types, or Attributes.
- Each Boss Deck has 1 card with a hidden effect.
- Boss Duel monsters (and the Tokens they Summon) are not the only Monster Cards that can completely lack Levels/Ranks, Types and Attributes. The 2 'monsters' placed on the field by "Magical Hats" also lack these properties.
- Boss Duel cards lack distinctive artwork, with the picture simply containing a symbol connected to the villain character who owned the original cards: Pegasus' Millennium Eye, Don Thousand's Emblem, and the masks of Nightshroud and Z-one.