Knockers are the Undead revenants of miners killed in accidents, particularly accidents caused by carelessness or greed. They are all but mindless and utterly hostile to those who have survived where they perished. Usual Knocker tactics are to try to get between working miners and the surface, and then strike at the wooden supports to collapse the tunnel whilst driving back those miners who try to escape. Single Knockers are usually destroyed before they can collapse the tunnel, but large accidents produce groups.
Knockers look like rotting corpses that have been crushed under tons of rock and then got up again. They normally carry mining tools and wear badly damaged miners’ overalls. It is sometimes possible to recognise them, but normally the body is too badly damaged.
Whilst Knockers seem to arise spontaneously, some people worry that there are Necromancers using them to disrupt mining and take the resources for themselves.
- Warhammer Fantasy RPG 2nd ED -- Knights of the Grail (pg. 80).