Eldritch Abominations are a a form of inhuman character, threat, or plot device, depending on just how inhuman they are. As a trope, they most commonly occur in the Cosmic Horror subgenre. Exactly what constitutes an Eldritch Abomination varies from critter to critter and setting to setting, but that undefinable indescribable unpronounceable nature is a good place to start. Eldritch Abominations aren't native to here, at least not if here is any place that normal folks (or humanity itself) belong. Most importantly, they are rare or unique. If an Eldritch Abomination becomes common place, then the concept has lost something - it's not just the Monster of the Week or a random Dungeon Denizen, it's mind-wrenching horror from beyond. Pure living Nightmare Fuel.
List of traits many Eldritch Abominations share:
- Tentacles, lots of tentacles
- Mismatched amalgamation of different species
- Draconic, squamous, reptilian, often winged
- Batrachian, amphibian, slick and slimy, bulging and inflating
- Molluscoid, octopoidal, (did I mention "Tentacles, lots of tentacles"?)
- Arthropodal, insectoid, crustacean, possibly with pincers or eye-stalks
- Osteicthyean, piscene, possibly with bulging fish eyes or heaving gills
- Indistinct, undulating, or ever changing.
- Literally indescribable, either not describable by human language or not parsable by human minds.
- Non-euclidean, possibly a result of higher dimensionality. See Alien Geometries.
- So bizarre it drives you mad just to look upon it. See Go Mad From The Revelation
- Alien and unearthly.
- Mentally alien, not driven by understandable terrestrial motives.
- Physically alien, it doesn't fit anywhere in our taxonomic tables.
- Not even based on folklore, it's just a random assemblage of weirdness.
- Resides (or is imprisoned) Beneath the Earth or at the Bottom of the Sea.
- Worshiped, summoned, or called by evil cultists.
- Slimy. May leave a trail of residue or mucous.
- Tentacles, lots of tentacles.
- Immensely huge.
- Extra or misplaced facial features. Too many eyes. Mouths in all the wrong places, etc.
- Distinct odor, which serves as a clue it was here, or as a brief foreshadowing just before it eats you.
- Bizarre abstract technology, math, and/or magic that our puny human brains can't understand.
- Tentacles, lots of tentacles.
- The works of H.P. Lovecraft feature many Eldritch Abominations.
- The RPG Call of Cthulhu has many such creatures in it.
- The spin-off Trail of Cthulhu RPG (which combines Call of Cthulhu with Pelgrane's GUMSHOE system) has excellent sections on the Gods and Monsters of the Cthulhu Mythos, along with advice on flavorful ways to use them (and hint at them) in an RPG, possible symbolic interpretations, clues to what's been at the crime scene, etc.
Game and Story Use
- Should be used rarely, so as to preserve maximum impact. When the monster defies all attempts at description, that should be a cue to the players that this is a threat to be taken very seriously.
- Entire campaigns could be based around trying to prevent ever having to encounter one of these things. If the Players are on their game, the cultists will be stopped before this thing is unleashed. If the players dither too much, they'll face one in the climactic showdown. If the players really blow it, the thing will have had time to awake, adapt, feed, and grow, and all the world will be in jeopardy.
- May be the last thing you see before waking up days later, uncertain how you escaped or where you've been.
- May be the last thing you see before going stark raving incurably mad.
- May be the last thing you see.