Beings formed from debris, fragmented souls, and the bones of those that have fallen into this world. When created, they will grow flesh in a warped mirror of how they'd have looked when alive. After a set amount of time, known only to them, they will seek the place they were created and allow themselves to rot. The process feels similar to sleeping. When they are comprised only of bones and other dry materials, they will continue about their life until the pull comes again, and they leave to regrow their flesh.
Rarely, this cycle will be disrupted, and the demon is unable to complete the transition from one to another. This renders them mortal. In this world, one must die in order to live, and the reverse is true. Without death, there is no life for them.
Giant, serpentine creatures with many limbs, antlers, and huge jaws. Their head is featureless, a bone-plate resembling a masquerade mask sprouting from the very tip of their snout. Masked Ones are responsible for the birth of all demons in this realm. Unlike normal creatures, they do not break down that which they consume. Able to steal souls with their eyes and bodies with their mouths, they grind everything up inside them and lash them together to create new and unrecognisable forms. They cannot be killed with magic, and must be physically cut open to release these creations - demons. Once they die, they revert into a tiny worm-like form, burrow underground, and begin to grow once more. The number of Masked Ones in existence is constant. They can never truly be killed, but new ones cannot be born either.
When a newly reborn Masked One breaks free of the soil, it possess only two limbs and the mask it is named for. At this stage, they can no longer rely on nutrients in the ground and must consume to keep growing. As they grow, they gain horns and more pairs of limbs. Ancient Masked Ones can be the size of mountains, with hundreds of limbs and antlers that branch as much as a tree.
The dominant religion promotes worship of Masked Ones and self-sacrifice for the chance to be reborn. Many Masked Ones do not even need to hunt, just sit and wait for the local sect to find it, and throw themselves into its maw. These demons are not actually being reborn, but rather, reconstituted into other individuals. It is, ironically, the truest form of death a demon can experience.
Worm-like creatures that share a hivemind, and come together to form superorganisms. They will incorporate objects in the environment such as sticks to bulk up their form and mimic other beings. Prey is quickly engulfed and digested externally.
(More to come!)