Spirit Torment

"Swinging the chain, swinging the chaaaain."

Deep beneath the surface of Shyish, the Realm of Death, there exists a structure known as the Great Oubliette. It is a literal continent-sized underworld that serves as a jail for the souls that ESPECIALLY pissed Nagash off. Miles upon miles upon miles of cold, dank, slimy, padlocked cells - think Azkaban from Harry Potter x1000. And the guards to that prison are Warhammer's equivalent of the dementors - the Spirit Torments.

The Torments are Papa Bones' pet jailers, torturers, and enforcers of his petty-ass will. In life, they were especially pitiless jailers that, in contrast with the rest of the Nighthaunt, got a pretty sweet deal - they essentially just have to keep doing what they were doing in life, just on a much grander scale. It's almost like Nagash has a soft spot for overbearing sadists who are way too cruel to their prisoners, or something. Their main ability that makes them such lethal gaolers is their ability to suck out their enemies souls and trap them within the large locks they carry around, before dropping them within the Oubliette. Being the sadistic bastards they are, some Torments will even peek in at their quarry through the keyhole, jeering at them for their terrible fate. This makes them a terrifying sight, even amongst the other forces of Death; after all, it isn't unheard of for Nagash to send them to capture especially unruly undead.

They used to stick to the Oubliette, sticking to their whole joy-sucking shtick until the Soul Wars began. The presence of the Stormcast Eternals - the faction that Bone Daddy has a massive, throbbing hateboner for - necessitated them. After all, the Torments are the only ones capable of capturing the souls of the Stormcast, who usually go crying back to Azyr upon dying so that they can be reforged. Instead, they end up getting trapped in the Torment's lock and get taken to their own special section of the Oubliette where they're... experimented on. It's never stated what's done to them, but this was the fate that befell a good portion of the Sigmarite Brotherhood Stormhost in the Broken Realms Saga. Whatever it is, it is not good.