Why didn’t Mimikyu ex’s Disguise Ability prevent damage from an attack?

Mimikyu ex’s Disguise Ability will not prevent damage from attacks in certain situations, as they are not affected by Disguise:

・ Attacks that ignore effects (such as Ledian’s Swift attack).
・ Attacks used while Abilities that nullify Disguise are in effect (such as Alolan Muk’s Power of Alchemy Ability).


Mimikyu ex’s Disguise Ability will take effect and prevent damage from attacks:

・ The first time it takes damage from an attack that does not nullify or ignore effects.
・ On the first attack after an Ability-nullifying effect has worn off.

For damage that doesn’t come from attacks, see the following FAQ. 

Why didn’t Mimikyu ex’s Disguise Ability prevent damage?