Atropus

"Atropus, known as the World Born Dead, is an undead planetoid whose coming is a harbinger of death and destruction.[...]"

Excerpt from an obscure tome of forbidden knowledge, "The Grimoire of Forgotten Realms".

Summary
Atropus worlds are living and dead, all at the same time. Experts disagree on their nature, some saying they are experiments while others insist that they are literal breathing planets. Flesh is the number one export of these worlds, followed by lovely and decorative bone. While they do have rough weather from time to time your biggest worry here is usually being really grossed out, but is also the enemies that roam the place. Specifically, the flesh reaper.

Codex description
A truly unusual type of world, Atropus planets are both living and dead. They are quite literally composed of flesh, and some even believe them to be sentient. Universally, it is thought that they are (and I quote) - pretty darn gross.

Notable Features
Upon arrival, the first thing the explorer will notice is that the surface of Atropus planets are literally Flesh and Bone. Though for amateurish eyes Atropus planets might look similar to Bloodstone worlds (even as far as to mistake the former for the latter), the veteran adventurer will immediately see that there are huge differences between the two, namely the eyes, teeth, functional organs, pools of organic poisons, digestive enzymes and rotting pus (ugh!). In defense of the inexperienced, though, it is important to state that some scientists theorize that Bloodstone worlds might be actually Atropus planets that are still in their "infancy".

Besides flesh, bone and large pools of bodily fluids, travelers can find the usual assortment of valuable ores and minerals, the veins growing richer the further down one mines (though mining in Atropus worlds is more of a flesh-cutting affair than a rock-crushing one).

As to the origin of these strange, maddening worlds, the experts haven't arrived at a consensus. Some believe that Atropus is simply the natural culmination of life's evolution: given enough time, the biosphere of a planet will eventually evolve from a multitude of interdependent livings beings to a single, planet-wide living organism. Others think that they are the results of advanced genetic engineering from some long-lost alien race, a lonely mad genius, or a long-lost alien race of mad geniuses. Yet anothers uphold more esoteric theories involving arcane-sounding things such as "Great Old Ones", "Primordial Evil", "Forgotten Lore", and "Embodiment of Madness"; a few of them even combine all of these weird concepts together!

Subbiomes
You can find these subbiomes on Atropus worlds: Hive, Alien Forest, Sulphuric Magma, Cellular Expanse, Red Waste, Fine Sand, Swamp, Blood Gulch, Hell Hive, Eldritch Field, Eldritch Forest, Dry Riverbed, Deadwood, Jungle, Magma, Savannah, Volcanic

Location
Atropus Worlds are located orbiting Black Stars and Dying Stars.

Trivia

 * Atropus worlds appear to be based on the Forgotten Realms planetoid of the same name.