When a Digimon with this card in its digivolution cards but without [Greymon] or [Omnimon] in its name attacks, does this card’s inherited effect activate?
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Official Ruling
Yes. You must activate this card’s inherited effect and use up its [Once Per Turn], even if the attacking Digimon doesn't have [Greymon] or [Omnimon] in its name. However, if the attacking Digimon doesn't have [Greymon] or [Omnimon] in its name, you can't reference DP or delete a Digimon.
Source: AD1-004 WarGreymon