Fern is a swampy biome with reeds and cattails, with muddy pools and short evergreen trees.
Terrain is flat rarely with hills.
Mobs & NPCsEdit
Slimes can be found above ground in the Fen. Passive mobs such as Cows and Sheeps will spawn.
Survival is easy because there is lot of trees and cows and sheeps spawn here.The dying trees can be farmed for persimmons, making a great early food source.
Exploring is safe because there isnt anything that can hur you, but mobs can hide under trees and in caves.
After BOP 2.0.0, Oak Trees changed to Dark Oak Trees and villages began spawn in Fen. Villages no longer spawn in Fen biomes, according to the most recent config files, but you can enable them by editing config file.