Zen Garden Mod by Leus allows you to set your own battles and fully customize them, select which characters to spawn and fight, what team you're on, what items you get, and even select which sound track to play !
Takes place in a new level the Arena of Hurt by EdT

discuss http://oni.bungie.org/community/forum/viewtopic.php?id=1351

Update by Samer
*can spawn newer characters
*more filters added
update can be discuss here: http://oni.bungie.org/community/forum/viewtopic.php?id=2454