LOL you made me felt like having a go at doing what you asked about. But using my thought of opacity mapping on the head and the spear and using my latest outfit.
Watching it now I see I should have added something like a capsule model to the inside of the neck so I could add blood texturing or something.
Also should have made the character look at his broken sword and shake his head after the other characters head finished falling....oh well maybe later I will do that and get the killers feet moving when he runs..



i7-3770 3.4GHz CPU 16 GB Ram   
GeForce GTX1080 TI 11GB
Windows 10 Pro 64bit

Here is a small tut with simplest method to break a prop in half in Blender with fairly nice outcome for adjoining parts.