Alir. Maximus Faustus. He'll be one of the bigger threats, unless he is dealt with in some way.

[ Already, Wen Qing has seen him eat twice, and she knows the others have seen him as well, tidying up after his... work, and generally trying to keep him in his human form. If only Messalina had picked a different demon, one who might play better in a human skin. ]

There are a few others who will likely cause trouble, but none stick out to me as the biggest threats we must deal with.