Trigon (TSHD-EN031)

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 to Special Summon this card in face-up Attack Position. While equipped to a monster by this effect, if the equipped monster destroys an opponent's monster by battle, select and Special Summon 1 Level 4 or lower LIGHT Machine-Type monster from your Graveyard. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed, destroy this card instead.)

Dragon / Union, The Shining Darkness