William Birkin pack

First 3 forms of William Birkin mutation. All include arms (for zombie plague, but it also should work with this plugin ), headless and head models (and  a decapitation plugin).

You need to add these lines in your sourcemod.cfg in order for decapitation to works correctly (you can change values):
//Decapitation
sm_decap_headshot "1" 
sm_decap_dmg "1500"
sm_decap_knife "1" 
sm_decap_he "1"