Crowley is canonically one of the godmodiest godmods that ever did godmod. Having said that, I obviously can't, and wouldn't want to, do anything to the character(s) of an unwilling player! In order to make things easier for all of us I'm going to explain a little of what he can do, as a demon, and then let you guys decide where you stand on things. Cool? Cool.
Sense desire: Crowley has the ability to scan the minds of humans (and possibly other beings) to determine what they desire, ranging from surface wants to their deepest desires.
Hypnosis: He can hypnotise a person with just a snap of his fingers, using this hypnotic state to learn what they know about a subject, influence their actions (though he usually prefers to let them make decisions themselves), and he can also rewrite their memories to a certain extent.
Possession: He can also possess those with some kind of occult inclination (psychics being the obvious example). The possession can range from a sort of co-habitation (or body-riding) to full-out control.
Suggestion/temptation: Humans sometimes flippantly say "The devil made me do it," but usually it's just a figure of speech-or a convenient cop-out. Sometimes, however, they are influenced by demons-a suggestion of doubt, an itch of temptation. It can be either through direct speech or from afar.
Aaand I think that's it for the mind control type stuff. Chances are I'll contact you regardless, if things are getting weird enough for these powers to come out, but I'd appreciate a "y/n/gtfo/ask first" anyway :)
Character name and journal:
Sense desire:
Hypnosis:
Possession:
Suggestion/temptation:
Anything else?