Here is my proposal for a setting, fished from
what was going to be an interactive webcomic.
Between realities is the Primordial Sea, a void where rigid order, formless chaos clash and the Ciath-Naka dwell.
Time works on "Homestuck" rules, where worlds have different separate timelines that occasionally enter with no real pattern. Some universes have different physics, and any entity from another universe inside those will slowly fall victim to Dimensional Adaptation, an effect where the physics of the native universe slowly stop affecting the object.
The Ciath-Naka are powerful beings who created the primordial sea by accident. Their forms are incomprehensible and they can create new universes from a straw thought. Occasionally they posses beings, pray that their will accepts defeat gracefully.
I'll just copy biomorphics information from the OP.
Biomorphics
All species are classified through the Biomorphics system. Instead of having a limited list of races, Eternal Dungeons can use any race from any setting, as long as the cosmology is compatible enough.
Clayborn
Clayborns are formed mostly out of water and carbon. They are widespread throughout the Primordial Sea. For some reason, different species of Clayborns tend to resemble wildlife from other Clayborn worlds. With an emphasis on a bilatirally symetric, five limbed form. Is this because of intervention from the Ciath-Naka?
Planimal
Planimals are similar to the Clayborns, except that they often have a cell structure that makes them slow yet durable. They often have photosynthetic abilities, although they are too weak to provide sustenance for the energy demands of most Planimals.
Viral
Virals hijack the cellular functions of other races to reproduce, often fatally for both subjects. Because of this, most virals are technically all-male species, although exceptions do exist.
Mechanical
Mechanicals are machines capable of free will and sometimes self replication. They are biologically simple compared to other Biomorphics, often leading to glaring weaknesses. Their physical and mental attributes, sometimes both at the same time, are stronger than others.
Lithical
Lithicals are formed out of silcon or carbon structures similar to natural minerals. They do not think or move quickly, but they are immune to high temperatures.
Etherial
Etherials are made out of pure, abstract concepts given form. Their pychology and pysiology often embody those concepts, sometimes to a horrifying degree.
Kinetic
Kinetics are rare, dangerous, and physically impossible. Their bodies are formed out of pure energy, often causing postmortem explosions. They feed off of raw kinetic energy.
Souls exist in all realities as an unalterable, indestructible concept. Souls can be studied and copied by the Ciath-Naka and similarly powered beings.
"Magic" works differently in almost every universe, and is immune to Dimensional Adaptation. "Magic" includes things like the Force from Star Wars or Kryptonite, by the way. "Magical" effects and immunities do not combine well.