The Twilight Swamp is a biome from the Twilight Forest mod. This biome is only found in the Twilight Forest dimension. It is very similar to the Vanilla Swampland biome, though the Twilight Swamp has Mangrove Trees and shrubs scattered throughout.
When the player comes to the Twilight Swamp before killing the Twilight Lich, they will be welcomed with a thick, dense black mist. Attempting to traverse the Twilight Swamp before killing the Twilight Lich will inflict hunger on the player, and the Labyrinth will be unbreakable. Killing the Twilight Lich will lift this curse and allow the Labyrinth to be explored.