This is a human in the final stage of that whole "ashes to ashes" thing. Well, part of one, at least. A human gets harder to keep track of when it's in powder form.
- In a pile of stuff in the tomb in The Daveyard mausoleum
- Looting the sleeping necromancer in the Shroomcave
- Possibly found in various Military Cemetery Burial Plots
- Possibly dropped after defeating the cultists at Reboot Hill