My opponent's Digimon was targeted by this card's effect, then it digivolved and now has more digivolution cards than my chosen Digimon. Can my opponent's Digimon now attack and block?

No, it can't. If the number of digivolution cards under the opponent's Digimon targeted by this effect is less than or equal to those of your chosen Digimon at the timing when this card's effect activates, the effect will continue, even if the target's number of digivolution cards later increases.

Marching Fishes rulings (BT14-092)

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

Effect: [Main] Choose 1 of your Digimon. Until the end of your opponent's turn, 3 of your opponent's Digimon with as many or fewer digivolution cards at that Digimon can't attack or block.
Security effect: [Security] 1 of your opponent's Digimon can't attack for the turn. Then, add this card to your hand.

Official Q&A

My opponent's Digimon was targeted by this card's effect, then it digivolved and now has more digivolution cards than my chosen Digimon. Can my opponent's Digimon now attack and block?
No, it can't. If the number of digivolution cards under the opponent's Digimon targeted by this effect is less than or equal to those of your chosen Digimon at the timing when this card's effect activates, the effect will continue, even if the target's number of digivolution cards later increases.
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.

Marching Fishes rulings (BT14-092)

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

Effect: [Main] Choose 1 of your Digimon. Until the end of your opponent's turn, 3 of your opponent's Digimon with as many or fewer digivolution cards at that Digimon can't attack or block.
Security effect: [Security] 1 of your opponent's Digimon can't attack for the turn. Then, add this card to your hand.

Official Q&A

My opponent's Digimon was targeted by this card's effect, then it digivolved and now has more digivolution cards than my chosen Digimon. Can my opponent's Digimon now attack and block?
No, it can't. If the number of digivolution cards under the opponent's Digimon targeted by this effect is less than or equal to those of your chosen Digimon at the timing when this card's effect activates, the effect will continue, even if the target's number of digivolution cards later increases.
Ruled Mar 28, 2024

Got a line that uses Marching Fishes? Map it in the builder and share it with a link.