| Side Deck
A Side Deck (Japanese: サイドデッキ Saido Dekki) is a Deck of up to 15 cards, separate from the Main Deck and Extra Deck. The Side Deck is used in Matches between Duels, to alter the contents of the Main Deck and/or Extra Deck. Side Deck is not compulsory, but can assist in duel against specific opponent.
- Before the Match, if using a side deck, show it to your opponent without revealing its contents. Just to let your opponent know if you use one, and the number of cards in the Side Deck.
- If using sleeve for Side Deck, they must match with the sleeve used for Main Deck, whether if the card would begin he duel in Main or Extra Deck.
- Side Deck can only be used during Matches, and only in the Matches' 2nd or later Duels.
- When using Side Deck to alter the content of Main Deck and Extra Deck, the number of cards in each decks must remain the same.
- At the end of the Match, any cards registered in the Side Deck must be returned to the side deck.
Common Side Deck cards include various forms of Spell and Trap removal, such as "Dust Tornado" and cards that can directly counter common strategies, such as "Prohibition", "Chain Destruction" and "Royal Prison".
Since a Side Deck is not compulsory, a value of 0 for a Side Deck is considered legal. In both the OCG and the TCG, any value between 0 and 15 inclusive is permissible.
The Side Deck is invaluable in tournament play. Facing certain Decks can be a walk in the park or a nightmare depending on the contents of your Side Deck.
Previously, the Side Deck could not be used to alter the contents of the Extra Deck, though this has been changed. This is done to better suit a strategy against an opponent's Deck.