how about an arena where it starts as a normal death match but in 2 corners of the arena there are cages with 2 other bots and 1 gets let out every minute? i know it's possible if you just look at the new bbeans arena the walls come down at a certain point in the match you just need the walls surrounding the bots in 2 of the corners in a new arena. would make a nice new match and you could draw the entry numbers in the hat or something xD
Possibly an arena like a reversed shell spinner, with weapons on the walls, a circular arena, and the walls spin around. Also, a hazard idea, jaws that hinge up out of the floor and smash together