Do cards trashed from my opponent’s security stack by this card's ＜When Attacking＞ effect activate their ＜Security＞ effects?

No, the cards weren't being flipped over by a security check, so their ＜Security＞ effects don't activate.

Gallantmon Crimson Mode rulings (EX2-073)

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

Effect: [When Digivolving] Delete all of your opponent's Digimon with the highest DP. [When Attacking] Trash the top card of your opponent's security stack. Add 1 to the number of cards trashed by this effect for every 10 cards in your opponent's trash.

Official Q&A

Do cards trashed from my opponent’s security stack by this card's ＜When Attacking＞ effect activate their ＜Security＞ effects?
No, the cards weren't being flipped over by a security check, so their ＜Security＞ effects don't activate.
Ruled Mar 28, 2024
My opponent has 1 or more cards in their security stack. I attack my opponent with this Digimon and its ＜When Attacking＞ effect trashes their last security cards, leaving them with zero cards in their security stack. If the attack isn't blocked and my attack is successful when they have zero cards in their security stack, do I win the game?
Yes, you do.
Ruled Mar 28, 2024

Combos using Gallantmon Crimson Mode

See these rulings play out in real lines, step by step.

Crimson Raid: Delete, Unsuspend, Strip Security

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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.