All its cards have to be face-down during the Duel, unless a card effect like "Convulsion of Nature" allows it. During the Duel, neither player may inspect either player's Deck, unless it is necessary due to a card effect or to verify that a player does not have a card that meets certain requirements in their Deck; in either case, the Deck must be shuffled after either player inspects it. Even if a card in the Deck is face-up, it cannot be looked at by either player unless it is on top of the Deck, in which case it is public knowledge.
Main Deck construction restrictions
Constructed Deck format
- The Main Deck must have only Legal cards.
- It must have a minimum of 40 cards, and a maximum of 60 cards. Only the cards in the Main Deck count towards this total.
- A Duelist may not have more than three copies of any Unlimited card included in their Main Deck, Side Deck, and Extra Deck combined.
- If a Forbidden, Limited, or Semi-Limited List is used, the number of copies must not exceed those requirements.
- Cards which have their name permanently treated as that of another card are considered to be the same as that card for this restriction.
Sealed Deck format
- Main Deck must be constructed using only card product provided at the event.
- It must have a minimum of 20 cards, the size may be raised to a higher number, but the size should never be below 20. There is no maximum size.
- A Duelist may include as many copies of any card he or she likes, even more than three.