8 official rulings from Bandai, last ruled Mar 28, 2024. Straight answers to how this card actually resolves.

Does "can't attack this Digimon and can't activate <When Attacking> and <When Digivolving> effects" in this card's <Opp Turn> effect apply to opponent's Digimon with as well as those with ?
Yes, all of your opponent's Digimon with either or are affected by "can't attack this Digimon and can't activate <When Attacking> and <When Digivolving> effects."
Ruled Mar 28, 2024
My opponent has this Digimon in play, and I digivolve one of my Digimon into a Digimon card that has <Security Attack +1> and a <When Digivolving> effect. Does that Digimon activate its <When Digivolving> effect?
No, it has <Security Attack +1> as soon as the digivolution is complete, so this card's effect prevents the <When Digivolving> effect from activating.
Ruled Mar 28, 2024
What kind of Digimon does this effect's "Digimon with " refer to?
It refers to Digimon affected by or effects.
Ruled Mar 28, 2024
If an opponent's Digimon has both <Security Attack +1> and so the values cancel each other out, is the Digimon treated as not having , and is it unaffected by "Digimon with can't attack this Digimon and can't activate <When Attacking> and <When Digivolving> effects"?
No, is not canceled even if a Digimon has both <Security Attack +1> and . The Digimon is considered to have , so the effect applies to this Digimon.
Ruled Mar 28, 2024
I digivolved one of my [MetalGreymon] into [BT9-015]/[MetalGreymon (X Antibody)]. It gets and +3000 DP with its <When Digivolving> effect, but does that effect activate when my opponent has this Digimon in play?
Yes, it activates. [BT9-015]/[MetalGreymon (X Antibody)] gains <Security Attack +1> from the <When Digivolving> effect, so after that effect has activated, this card then prevents further <When Attacking> and <When Digivolving> effects from activating.
Ruled Mar 28, 2024
If a Digimon has a effect that is only active when certain conditions are met, such as "While this Digimon has X or more digivolution cards, it gains <Security Attack +1>," does this card's <Opp Turn> effect apply when these conditions aren't met?
No, it doesn't.
Ruled Mar 28, 2024
My opponent has this Digimon in play. One of my Digimon that doesn't have attacks it, and then the attacking Digimon gains from a <When Attacking> effect or an effect such as "when one of your Digimon attacks". What happens to the attack?
The attack continues. This effect doesn't end or cancel an attack if the attacking Digimon gains after the attack has been declared. It prevents Digimon with from declaring the attack.
Ruled Mar 28, 2024
When a Digimon with attacks, does this card's effect stop "when this Digimon attacks" effects of those Digimon, such as <Raid>?
No, "When... attacks" effects are not <When Attacking> effects, so this card's effect can't stop them from activating.
Ruled Mar 28, 2024
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Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.