The doll exists in two forms, one which looks like Wakaba Mutsumi, and another one wearing Mortis' costume. They each represent their respective character in the Mutsumi/Mortis headspace when the other is in control of their shared physical body.
This tag should be used for both instances, and Mortis (costume) should be added to differentiate them. Mortis (persona) can also be added where the Mutsumi doll exhibits Mortis-like behavior as can be seen in post #8732883.
