“XYZ-Dragon Cannon” may only be Special Summoned through its effect.
“XYZ-Dragon Cannon” may not be Special Summoned from the Graveyard.
“XYZ-Dragon Cannon” is never considered properly Fusion Summoned.
Fusion substitution monsters may not be used to Special Summon “XYZ-Dragon Cannon.”
Face down “X-Head Cannon”, “Y-Dragon Head,” and “Z-Metal Tank” may be removed from play to Special Summon “XYZ-Dragon Cannon”.
“De-Fusion” may target “XYZ Dragon Cannon”. “XYZ-Dragon Cannon” will be returned to the Fusion Deck, but no monsters will be Special Summoned.
Netrep Q&As:
Q: If “X-Head Cannon” and “Z-Metal Tank” are on the field and “Y-Dragon Head” is equipped to “X-Head Cannon” through its effect, can the three cards be removed from play to Special Summon the “XYZ-Dragon Cannon”?
A: They would need to be monsters at the time you would remove them from play to Special Summon the associated XYZ Fusion monster. Curtis Schultz, 01/29/2004
Q: If “X-Head Cannon”, “Y-Dragon Head”, and “Z-Metal Tank” are used to attack the opponent, can they be removed from play to Special Summon “XYZ-Dragon Cannon” during the Battle Phase to attack the opponent once again?
A: You cannot perform the Special Summon of “XYZ Dragon Cannon” (per its instructions) during your Battle Phase. The XZ, XY, YZ, and XYZ can only be Special Summoned by the method written on each respective monster during Main Phase 1 and 2 of your turn only. Curtis Schultz, 02/24/2004