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

I played a Digimon with 5000 DP or less in a state where my opponent used this card's <When Digivolving><On Deletion> effect to give all of my Digimon -5000 DP. Can I activate my played Digimon's <On Play> effect before it's deleted by its DP becoming 0?
No, you can't. If a card is played at the same time as deletion by DP becoming 0, the <On Play> effect is triggered, but it can't activate because the card is deleted before it activates.
Ruled Mar 28, 2024
Do I have to activate this card's <End Of Attack> effect?
Yes, you must activate it whenever possible.
Ruled Mar 28, 2024
Does this card's <End Of Attack> effect also activate when my opponent has no Digimon in play?
Yes, it does.
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.