EDIT: While making this mod, I didn't realize that a multiplayer ultimate mod actually already exists. That one seems to be a lot more feature-complete, so you should probably use that one instead. Not going to delete this though just in case anyone wishes to use mine for anything.
Because I enjoy nothing more then making others suffer, I made a lua-based recreation of the secret ultimate mode.
Now, some of you may be asking, "What's ultimate mode?"
Hell. That's what ultimate mode is.
No rings, no shields, no checkpoints, and only one life. Make even one mistake and you're fucked.
...but now with friends!
I'd say to have fun, but you probably won't.