havea command challenge and if other person accepts go to battle arena only one group is allowed in arena and you fight when you win you get teleported back to spawn and lsoer dies MWAHAHAH
well...I can already see problems with this. I mean the whole teleporting to an arena thing, that was changed for V.2 because it caused problems. I think it might just be a bit too complicated. However, I could see something similar, in that when you challenge someone, you get teleported to the arena, however you are able to walk out of it instead. Only once its over, obviously. Also, make it so that people can't walk in on your match, and so that only 2 people can be in the arena at the same time, unless you add multiple challenges etc.
meh i think thatd be to mch trouble itd add to the realism of the game to just have two people fight eachother in the middle of nowhere , then the village leader of thhe losing ninja gets teh pissed and declares teh war gotta give people a better reason to declare war than what sora usually did which was hell im bored time to rape some random village. 'eeny meeny miny mo....'