Once per turn, during your Main Phase, you can equip this card to a "Machine-Type" monster you control as an Equip Card, OR unequip it and Special Summon it in face-up Attack Position. While equipped to a monster by this effect, that monster gains 500 ATK and DEF. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed, this card is destroyed instead.