Glyph of Disguise allows Rogues to pickpocket hostile humanoid NPCs and obtain their appearance.
Narcissa’s Mirror allows your pet to copy your current appearance.
Magical Pet Biscuit makes your pet twice as large.
However, Narcissa’s Mirror currently does not work on pets summoned from the Housing Pet Box , while Magical Pet Biscuit does not provide a permanent size increase . Its effect wears off after you leave the housing area for a certain amount of time.
If Blizzard allowed these two spells to work on housing pets, you could use a Rogue to pickpocket different humanoid NPCs and then permanently apply those appearances to your housing pets.
This would allow housing pets to effectively function as NPCs without requiring the developers to create an entirely new NPC system or UI . They would only need to expand and maintain the existing pet system.
This could also provide a huge variety of NPC appearances using assets that already exist in the game.