"The Great Darkness" (also known as The Darkness) is an unseen evil entity that threatens the livelihood of the Lemmings in Lemmings 2: The Tribes.
The First Sign...
"The Great Darkness" was prophesied to bring doom and despair to all the Lemmings. The Highland Tribe was tasked with watching for signs of "The Great Darkness'" approach. The first sign was a blood red sun that skimmed the horizon and shed cold, red light upon the startled faces that looked on. The Highland Lemmings trembled at the sight, for they knew it was a foreboding of evil. That was the day the sun failed and dawn crept from door to door in darkness......
- Paraphrased from "The Story of the 12 Tribes of Lemming Island"