An opponent's Digimon attacks using an effect at the end of their turn. Then, if this card was checked upon that Digimon's attack and this card was played using its [Security] effect, when do I delete the [Familiar] Token that was played by this card's [On Play] [When Digivolving] effect?
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Official Ruling
It isn't deleted at this timing, it's deleted at the end of your opponent's next turn.
Source: P-165 ShoeShoemon