Níðhöggr was, in Norse mythology, a serpent which lived in the depths of Niflheim at the roots of the world-tree Yggdrasil. Níðhöggr tries to destroy the foundations of the world by constantly gnawing at the third and largest root, but with no result since each morning the Norns, the three sisters who controls the fate of everything, heal the roots with the mystic waters from Urdarbrunn, the holy well of Asgard. The squirrel Ratatöskr is constantly running up and down the trunk of the tree exchanging insults between Níðhöggr and the giant eagle Hräsvelg which lives at the very top of Yggdrasil.

Fáfnir was the son of the dwarf king Hreidmar. Hreidmar received the cursed gold of Andvari as a repayment for the loss of his other son Ótr. Fáfnir and his brother Regin then killed their father to get the gold, but Fáfnir decided he wanted it all for himself and turned into a dragon to protect it. Regin sent his foster-son, Sigurd, to kill the dragon. Sigurd succeeded by digging a pit under the trail that Fáfnir used to walk to the stream, and plunged his sword Gram into his heart as he walked past. Regin, however, corrupted by the curse on Andvari's gold, planned to kill Sigurd to take the treasure for himself, but Sigurd, having eaten part of Fáfnir's heart, got the gift of understanding animals and was warned by birds of Regin's attack and ended up killing him instead.

In Norse mythology, trolls are ugly, malicious creatures and the enemies of mankind. They are much bigger and stronger than humans, and leave their caves only after dark to hunt. The trolls were also great shapeshifters, taking shapes of objects like fallen logs or animals, if they are exposed to sunlight they will instantly turn to stone. In later myths they are roughly the size of humans or elves, and thought to be the owners of buried treasures. The trolls sometimes abducted people to live as slaves among them. These poor souls were known as bergtagna (taken by the mountain), To be bergtagen does not only refer to the disappearance of the person, but also that upon returning, he or she has been struck with insanity or apathy caused by the trolls. Anyone could be taken by the trolls, even cattle. Occasionally, the trolls would even steal a new-born baby, leaving their own offspring, a changeling, in return.