I think that if you attack a monster, you should be the only one to get the experience and rewards unless you're in a party, then it's shared. Outside of party combat, then I think if you're getting your ass handed to you, then you should be able to receive assistance. I like the idea Leowilde proposed, but I would tweak it to say that if while in combat, you type out /helpme, then you get some emote that says "<character name> looks at <t> with fear and begs for help with defeating it." or something to that effect. Then, that monster has open season declared on it. This way, people who are fighting NM for the challenge can't have some misguided hero of justice swing and "save" the day, and people who really want the help can ask for it.