If you want impossible..Team deathmatch. 32 bots on each team.Huge arena, like the low lag arena but with fairly low walls. That would be fun. :P
Dude you KNOW there can only be 4 bots in any match. But Ian's new RoboZone arena does this to a degree.
It starts with 2 robots, then another robot joins after 30 seconds then the last bot joins after another 30 seconds. If a robot is destroyed within the 30 second period then the next one joins in.The arena comes with multiple modes including:*Rumble mode - every bot for itself.*Gauntlet mode - 1 bot tries to defeat 3 bots in a row.(Note: it's not actually my arena, it was created by Trovaner.)
https://gametechmods.com/uploads/files/Robo%20Zone%202%20AI%20with%20Arenas.zip
the AI aren't much of a challenge.