About this 1 vs many thingie.. why couldn't it be done?
In the series it happens very often that characters just aren't strong enough to hit another character effectively. They just stand there and absorb the punches/kicks/ki attacks like it is nothing.
If you'd take the player who has to fight all the other players, and disable a few normal things like being knocked away by melee, being knocked away by a heavy ki attack and give him a LARGE amount of health and powerlevel, and this would be easy to do.
This player would not fly when being punched and so would be able to easily counter attacks that are launched at him. Also give him like a 45% damage reduction so he wouldn't get mass beamed.
Also make it so that when he gets hit a large number of times in a short period, he would fly a little.(50% as far as normal.)
Now give this gamemode a max number of players who can enter (to make sure it stays realistic and the powerfull one has a good chance.) and you'd have a perfectly good gamemode.
Players would really have to work together like in the series to beat this guy. The one that kills him/ the one that did the most damage to him, gets to be the archenemy in the next round. (Every non archenemy player would have a certain number of lives.)
If the archenemy manages to kill of everybody before dying himself, he would have won. :fight:
If the coding/engine/etc would allow it you could even make a lill' sequence where the archenemy is allowed to fire a HUGE beam (not otherwise available) or ki ball at the map, and everything would get so bright you can't see the map anymore.(Like the solarflare effect.)
(EDIT: After he wins the match of course)
This would symbolise the destruction of the planet the other players were trying to defend.
Call the whole thing "Save the planet!" mode and voila...
Wheter or not people like the idea is a whole different thing, but i certainly think it could be done.. :]