I think you would need a remnant of the destroyed dementor itself, not just a cloak a dementor happened to be wearing when you killed it, and I don’t think dementors leave anything behind when you kill them.
I think you would need a remnant of the destroyed dementor itself, not just a cloak a dementor happened to be wearing when you killed it, and I don’t think dementors leave anything behind when you kill them.