The following rules apply to “XYZ-Dragon Cannon”, “YZ-Tank Dragon”, “XY-Dragon Cannon”, and “XZ-Tank Cannon”.
These monsters cannot be Special Summoned EXCEPT by the way described in their text. They cannot be Special Summoned with “Monster Reborn”, “Magical Scientist”, etc.
You must remove from play the monsters specified; you cannot use “Goddess with the Third Eye”, etc., because you are not performing a Fusion Summon.
You CAN remove a face-down “X-Head Cannon”, etc., from play to Special Summon on of these monsters from the Fusion Deck.
The Special Summoning of these monsters from the Fusion Deck has no Spell Speed and cannot be chained to (but can be negated with “Solemn Judgment”).