The invincibility glitch can be performed in the Multiplayer of Syphon Filter 2.
This glitch requires the combat knife and one of the two people hanging to a overhang. When these two requirements are satisfied the glitch is ready to be performed. Then, find a overhang to the height of the player (or the knife won't kill the opponent) and use the knife to kill the enemy and if correct, the opposer will fall due the death and when will respawn, will be invincible to every injury: to headshots to explosions. Also the knife or gas grenades won't kill the player. The only way is a fall from an height.