No Bonus, No Boarders, No Mercy!
Just a big battle pit (like the colusseum) Or a big battle field.
About 50-100 territs and any territ can attack any territ.
No Bonuses, not even territ bonuses. Just +3 per round or +5 or whatever.
Would be awesome on foggy!
Would be a test of diplomacy, army placement, and probability.

I know this pic wouldn't work, but invision a dungeon pit or something like this.