Bum is probably EXTREMELY dysphoric about their appearence because of the fact they are the boogeyman. And according to the legend, the boogeyman takes form of your biggest fear in order to devour you or your dreams.

This means nobody will see Bum the way they are. Bum is viewed as scary, terrifying. The weight of having to deal with multiple body structures and constant shapeshifting took all the energy they have. Thats why they are always tired, thats why you almost never see them awake.

Every single bone in this hellborn's body is broken and out of place. The only way they can try to make themself aproachable is to mask themselves in a child-like appearence to deceive other's eyes. They dont know who they are anymore. They refer to themselves in plural and 3rd person not because they are stupid, but because they no longer have sense of self recognition.