Permissions
~ threadhopping/threadjacking?
As long as the thread isn't marked private, go for it. If it seems to be a serious discussion, or you're not sure the best place to jump in, feel free to contact me first.
~ backtagging (commenting/threading on old entries)?
If it's your first tag to a post or comment, and the post is more than a week old, you might want to check with me first. Within a week, go ahead and tag! Even after a week, if we were already threading, I'm fine with backtagging as much as needed to finish out the thread.
~ Hugging this character?
Sure, why not.
~ Giving this character a kiss?
A friendly kiss on the cheek is okay. Anything else - Please stop molesting the angel. :(
(Fun fact: As of Season 5, Episode 3, Castiel was canonically a virgin. Whether he still is now depends on your personal preferences for headcanon and shipping. ;D )
~ Punching this character (provided they are given an opportunity to fight back)?
Sure. But unless your power levels are over 9,000, Castiel is just going to stand there and ask you why you did that. If a normal human tries to punch him, they might break their hand.
~ anything special for psychics/empaths/aura-readers/magic-users to notice?
Oh yes. Castiel is an angel, so that means anyone sensitive to the supernatural or divine should be pinging like crazy.
SPECIAL NOTE for any character who "sees" with senses other than their eyes: In Supernatural canon, a normal human who sees an angel's true form will have their eyes burned out of their head. This even happens to a psychic who tries to spy on Castiel from a distance. If your character is able to see someone's true form, psychic essence, aura, whatever, proceed with caution! Obviously Cas doesn't want to hurt anyone, but it's not something he can control. And of course it's up to you how much this would affect your character.
~ 4th Wall breakage?
Absolutely okay by me. Castiel will be confused, but he'll deal with it.
Permissions Post for Castiel to read minds and such is here.