Enter the master cheat ''BEWAREOBLIVIONISATHAND'' and go to a deathmatch. Select options, level, and characters as normal. Enter the match. Now go to the ''Warp'' cheats and select any level to warp to. Select it TWICE, because it won't send you there the first time.
You are now in a single player level with all your multiplayer options and players! up to 4 can join the fun, but it lags badly unless you only have 2 players.Warps do not work and you cannot pick up the single player items.
Try this on level 2, and with other cheats on
10/25/2004
Invincibility Glitch
If you are taken to zero health (death) as you fall into a save point, you will be able to exit the save point completely invincible. Your health will still be at zero, and the glitch will wear off if regenerate any health. As long as you keep your health at zero, you can stay invincible forever.