On how to run deep ones in Call of Cthulhu and why you should fear them

There's no reason to fear a typical deep one. The worst depiction of deep ones is as stupid animal male feminists in neonomicon. That's not what they're like at all. The average deep One is smarter than a human, but is a harmless eccentric who wants to pursue his or her studies and craft in peace. He also has been doing this long enough that the average deep one sculptor makes Michaelangelo seem like a talented amateur who might amount to something in a couple of centuries of apprenticeship.

That's not who's going to be chasing you around a lighthouse, however. The Deep ones are a race on the verge of extinction and, to some, this is intolerable. There aren't deep one nations anymore, but only isolated city-states. Outbreeding with unrelated species, such as humans, sharks, and whales, is just a desperate attempt to stave off the inevitable end. This doesn't bother the typical deep one because they're immortal and so they don't see what all the fuss about since most of their ancestors eight generations back are still alive and fine, but certain fanatics see the passing of the great race and will do anything to bring about it's return or drag humanity down with them.

A deep one isn't the creature from the black lagoon: it's the creature from the black lagoon as a dangerous psychic sorcerer-scientist with a chip on their shoulder and a well-deserved sense of racial superiority over the stupid prairie apes, a biongeneered body far superior to a human, and all the bitterness of a fallen empire, a decayed and degenerate culture, and a species nearing extinction.

In a straight-up fight a human with a gun can kill an unarmed deep one fairly easily, but that's why they never engage in a straight-up fight. They're smarter than the players and respect humans just enough to make their hatred personal.

Also they know a method for drowning a human that takes nine agonizing hours.