Curse of two faces

Touch an object with this curse and your mind will be split in two

You not only have yourself in you mind, but another completely different person

At first this person will just be a voice, but after one day they will be able to swap places who is in control.

After two days, rather than being your body, when the second mind comes in control, it will also change your entire body

After three days, your second mind will not only have their own body, but their own class as well

Their own body can be a completely different species than the original characters

Player, not character gets to choose who's going to be the second mind