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

This card’s effect reads, “if this Digimon has [MetalGreymon] or [X Antibody] in its digivolution cards”. Does having a card with [X Antibody] in its traits count?
No. This effect specifies a card name, so you must have a card whose name is either [MetalGreymon] or [X Antibody] in this Digimon’s digivolution cards. Having a card with [X Antibody] in its traits doesn't count.
Ruled Mar 28, 2024
After having digivolved into this card, I place an [X Antibody] card in this card’s digivolution cards later that turn. Does this Digimon get +3000 DP?
No. If a [MetalGreymon] or [X Antibody] isn’t in this Digimon’s digivolution cards at the time its <When Digivolving> effect activates, it doesn’t gain +3000 DP from its effect.
Ruled Mar 28, 2024
Got a line that uses MetalGreymon (X Antibody)? Map it in the builder and share it with a link.
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