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Salthri, the Four-faced Sephulcre
Those walls that Sossurl builds lead many to war, and there are times where two who hate each other by dint of those walls will slay each other. When they do, and proper funerary precautions are not immediately taken, their higher and lower souls are pulled to the wall the following dusk, and there are steeped in demonic magic until the next new moon, where at midnight from the rock crawls forth this thing, with two howling eyeless visages that shriek and tear endlessly, and two silent, mouthless masks with which it sees front and back. The wall will stand until it has released this thing, and if whatever quarrel it had started has been laid to rest, it will shatter promptly. Its skin is stone, the same basalt as the wall that birthed it, cracked and interspersed with dead flesh. It has four legs and four arms, and if left alone, these limbs shift about some, as though jockeying to move to the fore or the top. It knows no purpose but hate, and attacks all it can see, stopping only after it has slain a victim. Then its chest cracks in twain, and strong rocky arms place the body in this new maw, placing both body and soul inside it.
The Salthri does not gain any known benefits from this practice; whether it has interred a new body in itself or not does not refresh the dead skin inside it, nor does it curb its rage, or add new faces. The Salthri itself lacks the self-awareness to wonder why it does this thing, and even if it did possess that introspection, perhaps it would not be able to answer the question.