Side-story to "Jöttun's Apprentice".
Scathfanai was a dökkálfar warrior. His parentage is unknown. Since a young child he showed great aptitude in combat. Later, after completing his training, he wandered as a mercenary. During this time, he proved himself the greatest fighter. His fighting and combat skill were unmatched. He was then recruited to serve in Odin's court. There Scathfanai served as an inner guard of the Weapons room. He was specially put to guard the Casket of Ancient Winters, captured during the raid of Jötunnheim during the reign of Tenebris, 20 years prior. The other Æsir guard were jealous and so, banded together and convinced the Allfather to cast him out by portraying Scathfanai as a traitor. In retaliation Scathfanai stole the Casket of Ancient Winter when he left. During his time in hiding, he learned of its powers and how to wield ice and cold. He then fled to Midgard fearing someone would detect the Casket, and hid there disguised as a human. On Midgard he stayed for four decades, planning his revenge. After the four decades he returned to Asgard. There he tracked down all who conspired toward his banishment, and brutally killed them. During this time period of his banishment, Scathfanai used the Casket of Ancient Winters to hide himself from Heimdall. No one figured out who killed the group of guards, at least not until two decades later. After his revenge, Scathfanai returned the Casket in secret, as it was not safe to have anything of that power on Midgard. He then returned to the humans and sired a child, Muirgen. Muirgen's son, Kane, sired a child by a svartálfar. Scathfanai's line continued to be a mix of dökkálfar, svártalfar, and human.
A/N: Dökkálfar in Norse mythology means Dark Elf. Also svartálfar is a Black Elf in Norse mythology. There are theories that in Norse myths they are both names for dwarves, but in regards to the story they are two different kinds of Elves.