The image of the drekar coheres depictions in Viking Period runestones. The runestones under consideration date to the 1000s.
The monster stats conflate various Norse sources, including Níðhǫggr, Fafnir, Jǫrmungandr, the agony of Loki, and the icy venom of Élivágar. Unlike the cultures of other lands who compare snake venom to burning fire, the Norse of the Viking Period compare snake venom to stinging ice-cold water. The drekar ‘dragon’ is an ormr ‘snake’, and is specifically a naðr ‘adder’, albeit a monstrous specimen of this species. Another name for the ‘dragon’ drekar, is a ‘supple snake’ linn·ormr, namely a constrictor snake that wraps around its prey.
The snake mostly has watery imagery, being either in water or near water. It moves like water. It wakes from hibernation as the winter ice thaws, and supercooled waters flow from the mountains. There is also some earthy imagery, such as burrows, caves, graves, fields, heather flowers, and ‘grinding’ the roots and the fallen branches of trees. But even these earthier specimens are arguably near water. The drekar here focuses on the watery imagery, especially in light of the venom resembling ice water, and the notable drekar ‘dragonships’ that can ‘slither’ across the ocean.
The family of the hero Sigurðr is described as resistant to snake venom, and while nonexplicit in the battle scene, this resistance seems to help Sigurðr survive the venom from Fafnir. For purposes of D&D mechanics, the venom is already complex, with cold, psychic pain, and an incapacitation mechanic. For the sake of simplicity, poison as an additional damage type is ignored, and the mechanics emphasize the vivid aspects of the monstrous venom. Likewise, other D&D dragon breath weapons are versions of snake venom, but also lack reference to actual poison damage.
There are various Old Norse texts that describe vættir mysteriously appearing and disappearing. An alfr suddenly physicalizes in the midst of a crowded longhouse and vanishes again, becoming incorporeal. Jǫtnar manifest mysteriously from within heavy mists. A vættir takes the form of a goat that often wanders in, apparently from out of nowhere. An individual jǫtnar who is the sentience of a specific mountain in Norway manifests its mind into the form of a human, then marries a human and has children, travels to Iceland, abandons human life, and instead becomes the mind of a specific glacial capped volcano in Iceland. When called on, the mind of this mountain is able to visit the caller even from a great distance a way. Elsewhere, a shaman communicates with an alfr who is mentally present but that no one can see it except her.
A vættir is always the sentience of a specific natural phenomenon. A natural phenomenon can project its mind out of this natural phenomenon, even travel far away from it, to be mentally present elsewhere. Its mind can also manifest physically, and by having taken a form, truly becomes this creature physically. It can revert back into incorporeal mind, even as the sentience of a different natural phenomenon than its original source.
The vættir divide into ‘clans’ ættir, large families. Each clan groups together related phenomena. Humans too comprise a clan of vættir, where living human bodies are the natural phenomenon that has sentience. However the minds of dead ancestors have become corpses, and are no longer living human bodies, thus as the sentience of a different kind of natural phenomenon, change from the human clan to a different clan of vættir.
Note, grammatically, the names of groups are here in the Norse plural form, but treated in English as if singular or plural, such as one jǫtnar or many jǫtnar.