|This article contains canon information corresponding to the Tales of Arcadia franchise. That means all information in this article is true and has appeared/been validated officialy on-screen.|
The Eternal Night (also known as the Night Eternal) is a dark ritual that requires the dust of slain trolls to create a haze to enshroud the world and forever block out the sun so trolls would never have to worry about being turned to stone.
It was one of the primary goals of the evil sorceress Morgana to enact in her bid to conquer the world.
Gunmar was promised by Morgana that he would usher in the Eternal Night. He used those very words to rally sympathetic trolls and fellow Gumm-Gumms into his army, proclaiming that the Eternal Night would see trollkind reclaim the surface from humans. However, the rest of trollkind opposed his plan and Gunmar was imprisoned in the Darklands at the Battle of Killahead Bridge. At the same time, Merlin fought Morgana to stop her bringing about the Eternal Night and sacrificed most of his magic to imprison her in a secret chamber in the Heartstone underneath Arcadia Oaks, where no one knew she was. Merlin then went to sleep in his tomb, ready for the day they needed him again.
Hundreds of years later, when Morgana was freed with the Staff of Avalon, she used the Staff of Avalon and the ashes of several Gumm-Gumms to bring about the Eternal Night, enabling the Gumm-Gumms to invade Arcadia. Eventually, just as her spell was about to reach full strength and cover the Earth in eternal darkness, the Trollhunters managed to banish her to the Shadow Realm, enabling Merlin to regain his magic and put an end to the Eternal Night.