Drowned in Tar - fiction, mystery, post-apocalypses setting. [in progress]
Action takes place many many thousands years in the future, after a planet (presumably Earth) was infested with The Tar. Many creatures and plants were transformed by evolution, radiation or Tar itself. Atmosphere of the planet has weakened, oxygen depleted, seas and oceans almost dried out. Deserts, craters and canyons cover most of the known map.
The Tar (tar, sludge) - dark resin-like substance of unknown origin. Can transform any creature, consume any matter except, in seems, iron (Fe). Tar slowly devouring planet's crust, shaping new or copying the existing terrain.
Main creatures is this setting are the tarals - living beings transformed into monster-like creatures in the depths of Underground Tar Ocean.
Setting inspired by: various survival game concepts, Rain World (worldbuilding, creatures), Kenshi, Journey, Dune, Welcome to Night Vale (mystery), MadMax (landscapes, factions), Risk of Rain 2 (tar and claypots theme)