In my campaign I have a player who has, through some special means, acquired a sword gifted by Haela Brightaxe (the dwarven goddess of battle and luck). It was first just meant to be a reward for their deeds and respect toward her, and a curiosity since Haela is supposedly dead. Well, to my surprise, the party went down a path I didn't expect them to, which puts them in a situation where, if they are successful, they would be freeing a recently taken dwarven hold of an invading power. With that in mind, (and the fact that the character for RP reasons doesn't use the sword) I thought that I could give the sword a purpose to fulfill. Having seen events unfold, Haela gave to one of the few who pray at her altar an omen that battle for dwarven lands (the same events that caused her supposed death) is closing in once again. Now they are closing in on a point where if I'm going to act on this thought, I need something for this sword to do that might aid them in their conflict and give this sword some purpose. It doesn't have to be miraculous, but I want it to be in tune with the deity it's associated with.

A little background, I'll try to keep it short: A dwarven stronghold has fallen, enemies akin to the Shadowfell have taken over and hold the stronghold now with many of it's former residence either slaves, split and attempting to slowly weaken the enemy so they can reclaim it, or gone as refugees in bordering regions. Aside from slave labor the dwarves are also being used for experimentation, having their souls drawn from their bodies and stored away in crystals to serve their new masters in constructed bodies, many times irreparably damaging the soul. The leader of these creatures, would have a host of the dead risen from the corpses and because of his nature, shadows created from the ones that were killed at the time of the attack.

My first idea: When the sword strikes one of these incorporeal undead created from a dwarf, it makes a Wisdom save (perhaps only if it's the killing blow or at a certain hp threshhold and probably only a certain number of times a day, it's a rough idea) if it fails, the spirit of the dwarf is wrested from the control of its new master and reforms as a dwarven spirit that fights beside the wielder for a round before passing on but it seems almost too specific and only slightly fits the mold that I've layed out.

I would greatly appreciate any ideas or feedback from the idea I already have. I am lost for what I can do here. Thanks ahead of time and sorry for the long read.