OUT OF CHARACTER
Backtagging You bet
Threadjacking/threadhopping Please do
Fourthwalling I cant see why not.

ACTION
Fighting Yes. Agni is a very skillful fighter. He employs the use of the martial arts he learned in India but has been shown to pick up other fighting styles or skills swiftly.
Injuries Sure.
Killing I would probably want to speak about this before a fight would go this route.
Telepathy/mind-reading Perhaps. I can't see why you couldn't but I might want a message about it beforehand.

RELATIONS
Hugging Sure, Agni likes hugs. We're all friends here, right?
Flirting Yes, but he might not understand that you are indeed flirting. He's a little oblivious to such matters.
Kissing and/or other intimate actions Expect him to blush or be embarrassed if your character tries to kiss him, etc.

Anything else you'd like to make known? Agni is devoted to serving his God.. (Ie... Soma XD). He owes Prince Soma his life.