I really hope high level players cannot just grief kill people trying to level up their monsters. That would be fail.
Also, if it is PvP, can I charm other player-monsters?
Edit: Also, lets say I am playing as monster and I am in the middle of a battle with another mob, you are suggesting someone could just come up and kill me in the middle of a battle? I highly recommend rethinking the ability to avoid battling others because this present all sorts of problems. I don't think the dev team thought this through very well on the griefing side.