You have been cursed by some being that wants your true nature reflected back at you. Whenever you look into a mirror or have a reflection it is a horrid disgusting form which you have the ability to manipulate.
You must carry a mirror with you at all times through which you are able to summon this form to fight or assist you in some way. They function as a duplicate through which you are able to cast spells, use tools, take actions, ect. They share initiative with you.
Everytime you summon them you must roll a percentile dice and the Save DC will go down everytime you summon this form. If you fail the Save, the form returns to the mirror without problem. If you succeed the Save, the form takes your place on the plane of existence and you are forced into the mirror and the cycle begins again. The only way to free yourself is to be summoned and succeed the Save or by the Wish spell.
Since they are a twisted version of you they share all of your stats and abilities. They are just a duplicate for you to manipulate.
You can use this feat 3 times per long rest.