Tales of Tolgard
Undead dwarves are created by residual essence on the part of dwarves who are concerned, just before they die, that their final resting place will in some way be disturbed. It is this essence that allows the bodies of the dwarves to transform into protectors.
Undead dwarves appear in ceremonial burial armor and are armed with ceremonial weapons, yet their bodies look thin and desiccated, with fragments of bone showing, and stark white, wiry hair. They are corporeal creatures, yet they are faintly transparent. Undead dwarves speak any languages that they spoke in life.
Undead dwarves do not leave the place where they are laid to rest. If this place is violated, the dwarves appear from the very stones of their cairns/crypts by an innate phase door ability. This effectively gives the undead dwarves the element of surprise. Once they appear, they attack with their fists for devastating effect. Once intruders are driven off, they dissipate into nothingness with a tired sigh until the next desecrater appear.