Abonner for at downloade
Shadow Knife

Basically what it does is: with LMB you cut or backstab, depends on your and victims position. RMB jumps right behind your victim and forces you to aim to his back, there is minimum distance requirement to do the jump also jump costs 5 hp points, health will drop 5 points with each jump till you reach 5 hp.. Backstab one-shots the target, god mode is ignored because it doesn't do damage it just instantly calls death function.

Requirements:
Counter-Strike: Source ( for obvious reason )

Practical use of it.
Actually didn't thought much about it but as I imagine there are plenty of sandbox servers who could actually enjoy it ( battle between two or more players is actually fun ).
Maybe DarkRP servers would find way to use it i.e. bounty hunter but the code itself requires a bit more work to suit for DarkRP.

Down side:
Before jumping make sure there are no walls or any other indestructable objects behind target because you will get stuck in them.

Credits.
Arcane - for sharing CSS Knife Swep
Ecls - for helping me test

*Also.
If you find any errors, glitches please let me know in comments.

I could add an ability to get back to previous place by pressing "R" and it could solve the addon downside, what you think guys?

EDIT ( 2015 06 07 ):
*Added red glowing/smoking. ( Thanks to "♫さっぱりわからなく♫" for idea )