The Hydra is an Outer God which appears in the H.P. Lovecraft-inspired Cthulhu Mythos.
A malevolent extradimensional entity, the Hydra appears as a great pool of protoplasmic slime from which a forest of living heads sprout, screaming in torment. These heads come from a multitude of species from across all of time and space.
In 1783, an unusual 8-page pamphlet named On the Sending of the Soul with unknown origins appeared in the town of Salem, Massachusetts. These pamphlets circulated throughout the community, but most were eventually destroyed when they were linked to a series of gruesome murders.
What nobody had realised was that the pamphlet contained a formula for astral projection (involving a brazier and cannabis) which would transport the practitioner's psychic form to any destination he desired and was effective one hundred percent of the time. However, when the traveller reached his destination, any living beings in the vicinity would be immediately decapitated, their severed and still-living heads absorbed into the Hydra, their memories and life-essences adding to the creatures' already considerable power.
Afterwards, the unwitting reader would be transported back to his own body physically unharmed, although possibly traumatised by the experience.
Whether any copies of this pamphlet remain extant is unknown.
- The Hydra made its only appearance in the short story Hydra (1939), by Henry Kuttner.