I think “D&D PCs are fantasy heroes” is a feature, not a bug. A zero level commoner like the SoI narrator has plenty of reason to be afraid of 2HD Deep Ones. It’s just a matter of scaling the threat accordingly. So we bring in Cthulhu in person.
Pre-order bonuses are usually garbage. “You get the option of to dress your PC in this silly hat!” If they were good enough to sell they wouldn’t be giving them away.
Doesn’t matter. It was only scary in the 1920s because it was shocking to the audience. This audience isn’t going to be shocked. As for the PCs, they are used to non-human settlements, and half of them are probably hybrids themselves so they are hardly going to be bothered. The Deep Ones...
Pretty much anything in D&D, from a goblin up, would be horrifying if encountered in the real world. But to a fantasy hero it’s just another day at the office (see Conan).
You can horrify players with what the monsters (who might be human) have been doing though.
There is nothing paricularly horrifying about the genetic nature of Deep Ones.
PC Tiefling: "So, your daddy was a fish person? My grandpa was Dagon - the real one who is a demon lord. Would you like to see my tail?"
Sahuagin hybrids have appeared in D&D before, in Eberron for a start. And we...
As has been stated several times already, Cthulhu is confirmed to be the dark lord. And a key point is the Innsmouth domain is much larger than the town of that name. It’s like Barovia in that respect. The domain includes a large island on which the town is situated at one end, and, in true...