Extra Deck

The Extra Deck (previously referred to as Fusion Deck) is a Deck where Fusion Monsters, Synchro Monsters, and Xyz Monsters are stored during a Duel. They are separate from the Main Deck, and you can search through it to find a Fusion Monster, Synchro Monster, or Xyz Monster that you need. There was a 15-card limit to the Extra Deck, regardless of how many Fusion Monsters, Synchro Monsters, or Xyz Monsters you include. However, sometime during the 5D's arc the limit became 20, and when the "Numbers" came out the limit was removed completely. The "Maximum of 3 Rule" for cards of the same name still applies.

If a Fusion Monster, Synchro Monster, or Xyz Monster is on the field, in the Graveyard or is 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.

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