Ashen Dead
This marks a site of mass death by fire. While there are now no corpses to reanimate, the ashes of the unquiet dead have mixed together into a churning, moaning mass.
Magical Effect. This necromancy can be recognized with a Religion check, revealing that features such as Turn Undead and spells like hallow will suppress it.
Pained Cacophony. The wailing of the souls is constant and concentration checks have disadvantage .
A group Religion check to conduct a daylong funeral service puts the souls to rest, made with an expertise die with a Performance check that provides uplifting music, a eulogy, or the like.
Critical Failure: The ash is picked up in a sudden wind that coats everyone and leaves a distant screaming in their ears. Each adventurer suffers 3 (1d4+1) levels of strife and for next 2 (1d4) days has nightmares. While troubled by these nightmares an adventurer regains half the usual number of hit dice and cannot recover from fatigue or strife.
Failure: The adventurers fail to properly perform the funerary rites and each suffers 2 (1d4) levels of strife.
Success: The souls of the dead leave the area with the sound of a relieved sigh. Each adventurer recovers from a level of fatigue and strife.
Critical Success: The adventurers are blessed with what help the souls can provide and for the next 7 (2d6) days have advantage on saving throws against mental stress effects, fear, and becoming rattled.
Leave It Be
If the party leave the souls to their pained existence the undead lash out, triggering a Critical Failure