Mask of the Parallel

Wondrous item, Legendary, Requires attunement by a barbarian, cleric, druid, fighter, monk, paladin, rogue, or sorcerer
You can don this shiny white venetian mask as an action. When donned this way, the mask magically melds into your face and vanishes, changing your appearance and abilities. You can describe how your appearance changes, but this effect can’t disguise your identity or equipment.
When the mask activates, choose one of your classes that meets the attunement requirement. Your subclass for that class temporarily changes to a different one of your choice. You lose any features, proficiencies, and spells provided by your actual subclass, and gain the ones of the chosen subclass. You have full use of any limited-use features from the new subclass.
Each different subclass can only be used once, then the mask can never provide that subclass again, even for a different wearer. You can’t level up while wearing the mask.
You can remove the mask as an action. Once you do, you can’t activate the mask again until you finish a long rest. The mask can't be forcibly removed unless the wearer is unconscious.