Thought, as I reread HP & the SS: 2-3 Witches and an Infernal for a Monsterhearts con one-shot set at Hogwarts. No lack of sign-ups, that's for sure. The idea is that the Infernal is someone with no real magic power; they depend on their bargain to get them through their classes.
Could also see Lula's Genie as a non-student PC, once that playbook is playtested.
Instead of homeroom seating chart, you could have your DADA seating chart...