Based off the Shadow Miku ( http://steamcommunity.com/sharedfiles/filedetails/?id=312489252 ) model made by CaptainBigButt and Cra0kalo, this addon gives the Witch a light blur effect, and glowing eyes.
The blur (which is not actually blur, but a gimnick) and cloak effects are done thanks to the $cloakpassenabled and $cloakfactor VMT variables, which are the same that uses the Spy in TF2 for the cloak effect.
The model also has a faint "pulse" to make it easier to see, and glowing eyes instead of the default witch particles.
There are only two visual bugs that can't be avoided as they are caused by the $cloakfactor variable, but thankfully they are not game-breaking, and also infrequent:
-Whole model turning white-transparent (it depends on the environment effects, lighting and the location). Example: http://i.imgur.com/mtpuiOH.png
-"Nodraw" effect when looking her from far through a weapon scope. Example: http://i.imgur.com/G40rMqV.png