2 official rulings from Bandai. Straight answers to how this card actually resolves.

How long does the DP effect [ST2-01]/[Tsunomon] last?
It only exists when comparing the DP between two Digimon for a battle. It is not applied during the resolution "End of battle" or "On Deletion" effects that activated from that same battle.
I attack with [BT5-111]/[Omnimon X-Anti-body] that has this card as a digivolution card against a 16000 DP Digimon with no sources. Can I use its effect to delete that Digimon?
No, you cannot. The 1000 DP only exists when comparing the DP between Digimon for a battle. It is not applied during "when X attacks" effects.
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