Y-Dragon Head (DR1-EN060) - Dark Revelation Volume 1 Unlimited

Once per turn, during your Main Phase, if you control this monster on the field, you can equip it to your X-Head Cannon as an Equip Spell Card, OR change it back to a monster in face-up Attack Position. When equipped to a monster by this card''s effect, that monster''s ATK/DEF is increased by 400 points. (1 monster can only be equipped with 1 Union Monster at a time. If the monster that this card is eqipped to is destroyed in battle, this card is destroyed instead.)