A death anchor is a charm used by people to prevent their death, often used by necromancers.
A charm blessed by the God of death, Venmortsen, often crafted in his image with a bone between his teeth, forming a sort of anchor shape.

The anchor wil ressurect someone as an undead after dying, the necromancer can sort of customize the time it takes to be ressurected after passing, so you can find people in various stages of decay.

People who are undead can preserve their immortality further by braking off a part of their body, and preforming rituals on it, etching runes into it and blessing it, this can further increase their ability to regenerate when damaged in exchange for some of their power, which becomes more powerful with the more time one invests into this ritual, the proper term for this process is called a soul knot, or more simply you can call it a tether.
(Very powerful non-undead folk (such as mages) have pulled this off, but it is much harder for it to be successful this way)

The person can also reattach the tether, this gets rid of their regenerative boost in exchange for a power boost, it can be removed and put back in at any time.
This creates a big downside, if someone gets hold of this tether and incorporates it into a weapon, and example of this could be someone taking finger bone that's been turned to a tether, attaching it to an arrow and shooting it into the body of the being who went through this ritual, mortally wounding them and removing their ability to recover.