IT ENDS IN FIRE
The phrase "It Ends in Fire" is not a phrase you want to hear, but it describes in brief what could take centuries to explain - that the weapon system known as the "Sanguine" are very very very hard to kill.
The usual custom is to cut off their head, never look it in the eyes, and burn the entire body. Before or after a stake in the heart, is also a go-to option.
Well, you can accept the supernatural reasons, or stop and learn the science.
If any of the body remains, the Sanguine will simply re-assert its connection from the edge-dimension where its actual body resides, and reconstitute the entire body (or worse) in a matter of seconds.
If it can see you - even if the head is detached, it will know what to expect when it pops through the wall between dimensions. Putting it in a bag is recommended. A black bag. Lined with lead.
If any part of the body survives, the link between that local space and the Sanguine will continue to tie the two locations together. If the body can be destroyed by ordinary fire or gravity, this is your only chance while using conventional weapons.
The oak in the heart dampens and disrupts the resonant broadcast system used by most Sanguine to create the most terrifying effects and signal to its various body parts when the nerves are cut. Reliance on which tends to overwhelm the ordinary body when the link is severed, due to the ordinary control range that the nervous system carries during terrestrial operation.
Other impacts like brain damage, organ damage, lung impairment, broken bones, etc... do not have much impact on a being that is essentially operating the body like a puppet via a fly-by-wire neural network rig over quantum tunnels. However, like a drone, killing the body won't really intimidate the drone pilot sitting behind a wall of high energy on the edge of the this manifold and the next dimension. To really kill it, you need to shoot it with a weapon capable of piercing the veil and striking the actual cavity in space-time where the 'tick' is buried.
Personal sidearms made for this, using QSR power sources, can do this. However, the result can often be dramatically unfortunate since these pocket dimensions contain the collected mass of blood, bile, bones, bodies, entire oceans, living ecosystems full of things that live only in that dimension over millions of years, and ultimately could contain an ocean of lava or blood that is larger than most small planets. Thus, "offing" a Sanguine that has had time to mature is usually a planet-destroying affair best done form 1-2 light seconds distance (or more), and to the effect of burning the entire planet through the middle and out two orbits.
Still want to fight one?
You might want to watch "Lone Wolf and Cub", and listen for the sound of a "perfect cut" before you bury yourself in a river of blood like a fire hydrant. And that's if you wound one. Killing it may take more than one shot.
This is one reason very few of the weapons remain despite their ability to do the job. Most are buried under an ocean of blood. Telling your main man to have an ark waiting when you do is a good idea.