You cannot activate “Diffusion Wave-Motion” during Main Phase 2, or if you cannot conduct your Battle Phase this turn (if you activated “Soul Exchange”, etc.), or if there are no monsters on your opponent’s side of the field, or if your opponent has “Swords of Revealing Light”, or if your opponent controls 2 “Marauding Captains” (or appropriate monsters with “Raregold Armor”, etc.).
You cannot use “Diffusion Wave-Motion” and select a Level 7 Spellcaster-Type monster that was Summoned this turn with “Tribute Doll” because it cannot attack that turn due to “Tribute Doll”’s effect.
After you activate “Diffusion Wave-Motion”, if all monsters on your opponent’s side of the field are destroyed (with “Raigeki”, etc.) then your selected Level 7 Spellcaster-Type monster can attack your opponent’s Life Points directly.
When you activate “Diffusion Wave-Motion”, and your opponent chains “Ring of Destruction” to destroy your selected Level 7 Spellcaster-Type monster, the effect of “Diffusion Wave-Motion” is negated and your other monsters can attack normally that turn. But, if your opponent activates “Ring of Destruction” AFTER “Diffusion Wave-Motion” resolves (with no chain), and the selected Level 7 Spellcaster-Type monster is destroyed, your other monsters CANNOT attack.
If your opponent activates “Amazoness Archers” when your selected Level 7 Spellcaster-Type monster attacks, only the Level 7 Spellcaster-Type monster can attack because of “Diffusion Wave-Motion”’s effect, so your other monsters do not attack, but the -500 ATK effect of “Amazoness Archers” is still applied to all of your monsters.
If you Special Summon a monster during the Battle Phase after having activated “Diffusion Wave-Motion” (such as with “De-Fusion” or “Call of the Haunted”), that monster cannot attack because “Diffusion Wave-Motion”’s effect prevents all monsters other than the selected Level 7 Spellcaster-Type monster from attacking.
Your Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” must attack each monster on your opponent’s side of the field, 1 at a time.
After destroying all of your opponent’s monsters, your Level 7 Spellcaster-Type monster cannot then attack your opponent’s Life Points directly.
If your Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” has 1 of its attacks negated by “Magic Cylinder”, that attack is negated but your Level 7 Spellcaster-Type monster still attacks everything else.
If your Level 7 Spellcaster-Type monster equipped with “Twin Swords of Flashing Light-Tryce” is selected with “Diffusion Wave-Motion”, if it has attacked 2 different monsters using “Diffusion Wave-Motion”’s effect, it no longer gets the second attack from “Twin Swords of Flashing Light-Tryce”’s effect because it has already attacked twice.
If an opponent’s monster is equipped with “Ring of Magnetism”, your Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” must attack that monster. If the monster equipped with “Ring of Magnetism” is not destroyed (such as if it is also equipped with “Heart of Clear Water”), you cannot attack any of your opponent’s other monsters.
If you activate “Diffusion Wave-Motion”, and your opponent activates “Staunch Defender”, only the Level 7 Spellcaster-Type monster can attack, and it must attack the target of “Staunch Defender”, and it cannot attack any other monsters.
When a Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” attacks “Amazoness Fighter” or “Amazoness Swordswoman”, their effects are still applied normally at damage calculation.
You can activate “Injection Fairy Lily”’s effect when she is attacked by a Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” because her effect is applied during damage calculation.
When a Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” attacks “Spirit Reaper” or “Kisetai”, it cannot destroy “Spirit Reaper” or “Kisetai” (so “Kisetai”’s effect is not negated).
A Level 7 Spellcaster-Type monster selected with “Diffusion Wave-Motion” will negate: the Flip Effects of a monster it destroys as a result of battle, or the effects of “Giant Rat”, “Sangan”, “Dark Necrofear”, “Sinister Serpent”, “D.D. Warrior Lady”, “Wall of Illusion”, “Helpoemer”, “Marie the Fallen One”, etc.
Netrep Rulings:
Monsters destroyed by a monster affected by “Diffusion Wave-Motion” have their entire effects negated as long as that monster remains in the Graveyard.