L4D2 Versus Invisible survivor glitch
Play as undead survivor
Hold down Melee button while cycling through infected characters with right mouse button until you see cause menu to glitch and see "choose spawn location", then either switch to survivor team or wait till next round to respawn as a survivor.
1) After causing the glitch, DO NOT press right mouse button or you'll unglitch and/or lock ur key functions.
2) As undead survivor, your character menu will show you as dead, but you will still be able to play as a survivor with infected walking speed.
Credits for L4D2 Versus Invisible survivor glitch