Bayou is a warm, wet swamp biome. Fear Nightfall includes two separate Bayou biomes, one added by Biomes O' Plenty and one added by Regions Unexplored, plus a third Regions Unexplored variant called Old Growth Bayou. All three have swamp-style terrain. The pack weights each of them 6× in its horror biome selection, so they are among the more dangerous swamp terrain in the pack.
The Biomes O' Plenty Bayou has a temperature of 0.95 and a downfall of 0.9, and it rains. Grass is tinted #6faa50 and foliage #8bdb67, and the water is tinted #62af84. Its trees are willow-type: a willow log trunk two blocks wide, willow leaves, and willow vines hanging from the canopy. Trunks are 18 to 25 blocks tall. Ground cover includes ferns, large ferns, grass patches, cattails, lily pads, and sugar cane, and mud disks appear in the terrain.
Regions Unexplored Bayou
The Regions Unexplored Bayou has a temperature and downfall of 1.0 and also rains. Its grass and foliage use a purple tint from the mod's colour overrides. The ground in low-lying areas is mud, or peat mud when the mod's Peat and Silt option is enabled. Trees are cypress, placed where the water above the ground is no more than 2 blocks deep. Plants include flowering lily pads, elephant ear and fern patches, short grass, and shrubs.
Old Growth Bayou
Old Growth Bayou is a Regions Unexplored variant with a temperature of 1.2. Its ground cover is denser than the standard Bayou: dense ferns, dense elephant ears, dense short grass, and a giant lily feature. It has its own tree group and mud ground. Regions Unexplored assigns it through its swamp grouping, but it has no entry in the overworld biome table. Its humidity threshold lies outside the usual range of climate noise, so it is unlikely to generate in ordinary play (inferred from the mod's grouping rules).
Generation
Biomes O' Plenty Bayou covers about 0.15% of the land in the Fear Nightfall world, and about 0.05% of the cave layer at Y = -30. Regions Unexplored Bayou covers about 0.31% of the land and about 0.02% of the cave layer at the same depth. The pack weights both at 6× in its horror biome selection. The pack also places horror structures about 30% closer together, so Bayou terrain has a higher density of graveyard, hexerei and witch-hut sites than most non-horror biomes.
The Biomes O' Plenty Bayou sits beside Floodplain in the mod's overworld layout. The Regions Unexplored Bayou is placed in the swamp region of the vanilla climate split, where the temperature falls between -0.1 and 0.2.
Features
Willow trees (Biomes O' Plenty). Two or three trees are placed per chunk, weighted 4 to 1 toward two. About 30% of the trees are a medium variant. The willow vines are climbable.
Cypress trees (Regions Unexplored). Four trees are placed per chunk, where the water is no more than 2 blocks deep. Each tree needs a cypress sapling to survive on the spot.
Lily pads. Biomes O' Plenty Bayou has lily-pad patches. Both Regions Unexplored Bayou variants have flowering lily pads, and Old Growth Bayou adds giant lilies.
Ores. Both Bayou biomes generate the standard overworld ore placements (coal, copper, iron, gold, redstone, lapis, diamond, and others), so resource gathering works as it does elsewhere.
Fire. Fire burns out more quickly here than in most biomes, because the biome carries the vanilla increased-fire-burnout tag.
Water. The biome has the closer water fog effect, which shortens underwater visibility. Bayou water is also listed among the dirty-water biomes of Tough As Nails.
Mobs and structures
The Bayou biomes spawn undead and horror mobs. The generated tables below list every species and its weight for each Bayou biome. Notable hostile mobs include Ghoul, Skeleton Creeper, Decaying Zombie, Necromancer, and the horror-tier mobs Nightmare and Dread Hound. Surface slimes can spawn in the open because the biome allows surface slime spawns, and Slime Golem also spawns here.
Regions Unexplored Bayou adds wolves and a wider range of fish to its spawns, including tropical fish. Biomes O' Plenty Bayou spawns pigs and frogs as passive mobs.
Structures that can generate here include Haunted House, Catacombs, Mangrove Hut, and Covens, along with dead trees, mineshafts, and a range of village and mod ruins. The full lists are in the tables below.
Tips
Carry spare light and fuel. Fire goes out faster in this biome, and the horror mobs are heavily weighted here.
Bayou water is dirty for Tough As Nails. Purify it before drinking.
Expect Corpse Fish in the water. They are among the water mobs that spawn here.