Henry Kuttner Deities - The Hydra

The Hydra

There are innumerable tales of multi-headed monsters, all springing from the actual entity of whose real existence a few have known through the ages. This creature did not originate on earth, but in the gulfs Outside. It was... a vampiric entity, living not on the blood of its victims but on their heads—their brains... Through the eons this being has ravened in the abyss beyond our dimension, sending out its call to claim victims where it could. For this entity, by absorbing the heads and brains of intelligent creatures both of this world and of other planets, emerges with its powers and vitality greatly augmented.
—Henry Kuttner, "Hydra"

The Hydra dwells in an alternate dimension and appears as a vast sea of gray ooze. A multitude of living heads, some human and some alien, sprout from the ooze, sobbing and grimacing as if in great agony.

The Hydra's worshippers trick others into sending the god sacrifices through a pamphlet known as On the Sending Out of the Soul. The last page contains a magical formula for astral projection. When followed, the formula always works as expected, harmlessly transporting the user in astral form to whatever destination is desired. However, unbeknownst to the user, the ritual also brings the subject into contact with the Hydra, which then merges with the individual's astral self, using it as a host. Anyone present where the astral traveler appears is decapitated, the victim's head taken to become part of the Hydra. Afterwards, the astral traveler is returned safely to his or her original body, suffering no ill effects, except perhaps receiving a terrible shock from the grisly scene so witnessed.