Disguise acts as a limited but automatic substitute. It blocks the first hit on the ability holder, but unlike Substitute, it does not prevent additional effects like paralysis. Disguise does not protect against entry hazards, status moves or Pokémon with the ability to ignore abilities. If the user is confused and hits themselves, the disguise is busted instead. it remains in Busted Form if it is switched out, but reverts to Disguised Form outside of battle. If it faints and is revived, it will be revived in its Disguised Form and Disguise will be able to activate again.
Disguise cannot be copied by moves like Role Play or abilities like Trace. Disguise cannot be replaced using Simple Beam, Entrainment, Worry Seed, etc. One with Disguise will only get the ability Mummy if it is in its Busted form. Items like Weakness Policy will not activate since it is treated as a neutral hit under Disguise. Air Balloon will pop even if Disguise is active though.