I have seen in one of your interviews that it will be open so that anyone can attack a monster, and that whoever does the most damage will receive credit.
I would like to suggest using mob claiming like FFXI has. This guarantees that your party receives no outside help if it is unwanted, it allows you to control power leveling if you so choose, it creates no ambiguity about whose monster it is, and it creates a very fun dynamic for the parties puller/ranger.
I know you guys commented that player rep would keep kill stealing from happening, but I can see this game being large and the larger the game the less people care about their rep, if they care about it at all. One thing I always found myself doing is partying with the less desirables out of shear utility.
I wanted to give my thoughts and then see what others thoughts are on monster claiming, free for all, or even a mechanic that hasn't been tried before. Not trying to incite riot just want to get the ideas flowing.
http://www.pantheonmmo.com/content/forums/topic/4712/about-mob-tagging-stealing/view/page/11
We have a thread on this already . Wow , im on the other side of this one for once :)
As Xxar kindly pointed out, we already have an 11-page thread about Mob Stealing: http://www.pantheonmmo.com/content/forums/topic/4712/about-mob-tagging-stealing/
For that reason I will need to close this thread, please in future use the search function as more often than not you will find that over the 3 years of development that someone has already posting the same idea/suggestion/question etc. :)