Fen is a swampy biome with reeds and cattails, with muddy pools and short evergreen trees.
Mobs & NPCsEdit
Slimes can be found above ground in the Fen. Passive mobs such as Cows will spawn.
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.