Originally posted by hazelrah:

moder may have actually been a response to the cult of the wolf using fire magic.

The most common mountain runestone refers to wyrms as "Ymir's kin", so they likely predate the cult of the wolf (Fenrir being spawn of Loki) by a long time.

Originally posted by Fzanco:

Yeah I didn't think bonemass was Jotunn but maybe the supernatural essence of the Jotunn remains formed the amalgamation of undead which became the abomination bonemass?🤔

The swamp runestones don't refer to the ancient civilization destroyed and buried by the gods as jotun.

If the altar of Biomass is a mere construct and not actual remains of a formerly living creature, it could always have been fashioned after jotun remains by worshippers or other like-minded folks.