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 ! All in a brand new level: Junkyard by EdT

Will allow you to easily spawn and fight any character including custom characters like Iron-demon, Sarai, Motoko, Casey, Rayman ... (provided you have these characters installed)

For Instructions on how to use this mod,
1. Load the junkyard level (it's level 15)
2. Activate developer mod (Press F1 then x then F1)
3. Press ~ to bring up the console, then type help in the console and read the on screen instructions.

Or visit this thread for detailed instructions, more info, screenshots and support.

You can see a preview of the level in this YouTube video.

Credits: Updates to support newer characters by Samer, original concept by Leus, adapted to Junkyard by EdT.