system
Given the following post, respond as if you're commenting on Reddit:
human
[Call of Cthulhu] What were the beings Jack met/became under the farm and before entering the city of Dagon?
gpt
Those were Yithians, also known as the "Great Race of Yith" in some other works. They existed over 200 million years before humans did, and had strong psychic abilities and precognition. Yith itself was destroyed in a war against another, evil race known as the Flying Polyps (seen themselves in the game), but the Yithians were able to escape their fate through a limited form of time travel. By sending their consciousness forward in time they could swap minds and inhabit the bodies of species from the future, including humans. The minds of creatures hosting a Yithian are transported back to Yith in their place, where they basically can enjoy a relatively normal life (by Yith standards) once they overcome the culture shock. By doing this the Yith have gained untold amounts of knowledge about nearly all species both past and future, and store it in great libraries which visitors can access in exchange for cooperation with the mind swap thing. When the Yith eventually swaps back the host loses all memory of their time with the Yithians, save for scraps and bits of knowledge in dreams.

As said, Yith was eventually wiped out but the species lives on in some form. Knowing their doom was unavoidable the entire species up and disappeared. No one knows what became of them, but it is speculated they may have swapped with some other species from the far far future. Most physical traces of the Yithian society have been lost to time, but be careful who you talk to, lest they be a Yith in disguise.