If I choose an opponent's Digimon for this card's [When Digivolving] effect, and that Digimon loses <Blocker> due to digivolving, <De-Digivolve nocategory> (Trash up to nocategory cards from the top. You can't trash past level 3 cards.), or some other reason, can that Digimon now attack and block again?
No. Once a Digimon with <Blocker> is targeted by this card's [When Digivolving] effect, it becomes unable to attack or block until the end of your opponent’s next turn, even if it loses <Blocker>.
Mar. 28, 2024