The smaller caves of the between.

The between barrens are large open caves vaguely resembling the nether

The crimson between is the living flesh of the dimension and host to more powerful enemies such as fleshtenders and veinmakers.

 This biome also has "bone organs" and "blister lights" as its trees.

Gurshroom forests are home to the Gurshroom mushroom trees

Gurshroom forests have a higher spawnrate than normal for sentinel enemies.

Purple Gurshroom forests are home to the Purple Gurshroom mushroom trees ;

Purple Gurshroom forests are far rarer than their green counterparts.

The frozen sectors have no mob spawns other than the occasional reaver. However, players who venture into the frozen sectors will slowly freeze to death if not wearing Leather armor.

The volcanic between is a barren wasteland biome made primarily from "glassed betweenstone"

Assassin drones spawn here often.

Salt flats are rare biomes that spawn in the between lowlands

The salt flats have an increased spawn of siphonixes

Mudlands are rare biomes that spawn in the between lowlands

Mudlands are host to Protaxis mushroom trees

Like the salt flats, Mudlands  have an increased spawn of siphonixes