The Nidhogg
An Interplanar Serpent of Malice
These serpentine draconic creatures can be found across the multiverse, but most commonly make their nests in the coldest and most remote corners of the Shadowfell and the Lower Planes. This preference seems to come from their preferred diet of corpses and souls. While nidhoggs are primarily scavengers that feast on buried corpses, they are also known to supplement their diet by hunting. When it decides to hunt, a nidhogg will travel to another plane of existence as a precaution to not lead other creatures to its lair. Once on this new plane, a nidhogg will remain there for no longer than a day. In that time, it will cause as much damage and death as it can, bringing fresh cadavers back with it as food stores.
A nidhogg is a solitary creature that prefers the company of quiet graves and echoing caverns to that of any other living being, including its own kind. Nidhoggs will leave their nests soon after laying a clutch of eggs, never to return. They will abandon any stored food they might have alongside their young and travel to a new plane of existence before creating a new nest. Once the first nidhogg egg hatches, it will instinctively dispatch its siblings and claim the nest as its own, quickly growing in size and power.
Illustrated by Therése Pierrau
When I started to design the nidhogg, I had initially treated it more like a classic dragon. Parts of of this early design pass still remain in the monster’s stats, such as its Grave Breath and its Legendary Resistance.
Luckily I showed the concept to one of my coworkers before continuing the design and they were able to give me a new perspective. He has a background in northern euroupean history and we had a discussion about how most Norse dragons are much more serpentine in nature and how I may perhaps shift from a classic dragon to something more along the lines of the source material. He was able to also point me to some specific passages in the norse poetic eddas that reference nidhogg for me to draw upon. Its thanks to the eddas that I was able to put together its spell list, Shadow Stealth Bonus Action, and Corpse Consumption Legendary Action.
Next I looked back at the serpentine aspects of the monster and decided to add poison to its standard method of attack, as well as giving it a Constrict ability similar to the Giant Constrictor Snakes that already exist in D&D 5e.
Finally, its Realm Walk Legendary action was partially inspired by the mythology around how nidhogg chews the roots of the world tree and partially by its appearance in the video game God of War: Ragnarok. This would make the monster hard to pin down and give it some extra mobility options to hopefully create a fun and dynamic combat encounter.