Extra Deck

The Extra Deck (エクストラデッキ, Ekusutoradekki; Chinese: 特別牌組 Tèbié Páizǔ "Particular Deck"), previously referred to as Fusion Deck (デッキ Yūgō Dekki), is a Deck where Fusion Monsters, Synchro Monsters, and Xyz Monsters, as well as Pendulum Monsters that would have been otherwise sent from the field to the Graveyard, are stored during a Duel. They are separate from the Main Deck (minus Pendulum Monsters), and you can search through it to find a Fusion Monster, Synchro Monster, or Xyz Monster that you need. There is a 15-card limit to the Extra Deck, regardless of how many Fusion Monsters, Synchro Monsters, or Xyz Monsters you include. Pendulum Monsters placed on top of the Extra Deck by the game mechanics are not counted for the 15-card limit. The "Maximum of 3 Rule" for cards of the same name still applies.

If a Fusion Monster, Synchro Monster, or Xyz Monster that is on the field, in the Graveyard, or banished is returned to its owner's hand or Deck, it is instead sent to the Extra Deck, since Fusion Monsters, Synchro Monsters, and Xyz Monsters cannot exist in either the hand or the Main Deck.

The contents of your Extra Deck are not public knowledge to your opponent, and only you may look through its contents. During a Duel, the Extra Deck is placed face-down in the Extra Deck Zone.

Any card or card effects that still refer to the Fusion Deck now apply to the Extra Deck.

Limits on the amount of cards that are stored in the Extra Deck in the anime and manga are not yet determined.
 * It is also not clear at all times of the series if the Extra Deck exists in those Duels (such as early games shown just fuse monsters, without ever apparently pulling the Fusion Monster card from anywhere).
 * It is also not clear at all times where the Extra Deck is kept. In some instances the cards are not seen to be played from anywhere but the Fusion Card is present on the Duel Disk such as with Jaden Yuki, while other Duelists such as Akiza Izinski can clearly be seen to have Extra Deck zones built into their Duel Disks. In Yu-Gi-Oh! ZEXAL, the Extra Deck is stored in a box on the Duelist's belt, while in Yu-Gi-Oh! ARC-V, Duel Disks are specifically shown to have a compartment to store their Extra Deck in.