As the Demon is a master user of illusions, it'd be really handy if anyone interacting with him might fill out this form to let me know what I should and should not do! Would hate to step on anybody's toes.
The illusions don't affect inorganic creatures; anyone with a magical or supernatural ability will probably be able to detect them, if not break through them. If your character's not one of those, however, chances are (unless they have a firm connection to reality - will and determination don't matter!) they may be caught up in them. So ...
Is your character affected by illusions?
-- If yes, are you alright with them being used to terrify your character?
-- If yes, are you alright with them being used to herd your character places?
... Aaaand that's it. I'm fully alright with the Demon being attacked for his (admittedly tiny) monstrous appearance. Thank you!