Heavy Mech Support Platform (DR3-EN071) - Dark Revelation Volume 3 Unlimited

Once per turn, if you control this monster on the field, you can equip it to a face-up Machine-Type monster on your side of the field as an Equip Card, OR unequip it and Special Summon it in face-up Attack Position. When equipped to a monster by this card's effect, that monster gains 500 ATK and DEF. (1 monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed, this card is destroyed instead.)