XYZ-Dragon Cannon [DP2-EN014] Rare

"X-Head Cannon" + "Y-Dragon Head" + "Z-Metal Tank" This card cannot be Special Summoned except by removing from play the above cards on your side of the field, (You do not use "Polymerization".) This card cannot be Special Summoned from the Graveyard. By discaring 1 card from your hand, destroy 1 card on your opponent''s side of the field.