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

This card has an effect that activates at both <When Digivolving> and <When Attacking> timings. What does this mean, exactly?
It means the effect can be activated both <When Digivolving> and <When Attacking>. You can activate it as a <When Digivolving> effect when you digivolve this Digimon, then activate it again on following turns as a <When Attacking> effect by attacking with this Digimon.
Ruled Mar 28, 2024
This card has a <When Digivolving><When Attacking><Once> effect, but can I activate it twice in the same turn by both digivolving and attacking?
No. No matter which timing the effect is triggered at, it is still the same effect and can only be activated <Once>. If the effect has been triggered at <When Digivolving> and activated, it can not be activated again on the same turn, even if it's triggered <When Attacking>.
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.