The EX Pocket (Extra Pocket) is an extra slot players have in their hands. Both players have two slots in their EX Pockets, where they are visible to the opponent at all times during a match, however, the specific card(s) in the EX Pocket are not shown to an opponent at any time.
Some Abilities make cards spawn or "go back" to the EX Pocket, in the case of the EX Pocket being full, the card that is meant to be spawned or brought back will not arrive.
Once a card is played from the EX Pocket, another card will not be drawn in the slot. Both player's EX Pocket also start empty at the beginning of a match.