Threadhopping with this character?: Sure. It'll be exciting.
Backtagging with this character?: Sure! I get distracted and I'm old so I forget things /sob Backtagging is most welcome.
Hugging this character?: Yeah, sure. I don't know how much Crowley will appreciate that.
Flirting?: Rofl. You want to flirt with a demon of temptation, be my guest.
Kissing?: We'll have to see about this one, probably not though.
Relationships?: Haha yeah right.
Attacking/hurting/killing him?: Talk to me about this one. I like abusing my muses but some things need to be discussed.
Death, I'd prefer to avoid. Again, if your character has a reason to want to kill him, ask me and we can see where that might go.
Is there anything you do not want mentioned near this character?: Hell. Lucifer. Anything related to work, what, it's vacation time isn't it?
Is there anything you need us to know about interacting with this character?: He's a demon and he's got a pretty odd view of the world as it is. Humanistic stand point aside. He also might get all philisophical with you and religious so if you don't like that sort of thing I suggest you steer clear.
Now as for Crowley's abilities he has a few:
× Desire reading - It's implied that Crowley has some mind-reading ability, or at least the ability to sense the desires of others. "Every desire in his head was for a real gun." As the quote from the book goes. He can give people what they want.
× Hypnosis - Crowley can hypnotize people with the snap of his finger.
× Physical removal - Crowley can abandon his physical body and 'possess' another. Or simply make himself smaller.
× Spring cleaning - "Then he began to smile. He snapped his fingers. A pair of dark glasses materialized out of his eyes. The ash vanished from his suit and skin. What the hell. If you had to go, why not go with style?" Quote shows he has the ability to fix relatively small incurred damages to his person. The power cap sees to it that they're only small damages and not massive miracles being worked.
What this means for you character is that Crowley can possibly read their desires for whatever it is they want most, and possibly even give it to them.
Feel free to reply with anything you want done or would not like done to your characters. And if his mind reading will work or not work on them.