Y-Dragon Head (SDKS-EN006) [Structure Deck: Seto Kaiba]

Once per turn, you can either: Target 1 "X-Head Cannon" you control; equip this card to that target, OR: Unequip this card and Special Summon it in face-up Attack Position. While equipped by this effect, the equipped monster gains 400 ATK and DEF. (A monster can only be equipped with 1 Union monster at a time. If the equipped monster would be destroyed by battle, destroy this card instead.)