The monster of the poles & The god among us

First some worldbuilding (not part of the actual prompt) Theros is an ocean world, it has 2 suns, and its an earth-like world. It has 2 moons, the first one isn't reflective and is hard to see, the second is, and is well to be seen. The atmosphere closely resembles earth's atmosphere, and it has 1 mountain which is above the surface. There are a few main species on the planet, humans, cave crawlers, floaters, there are a lot more under the surface, and also on the surface, these could be mentioned from time to time.
prompt 8. A myth about a mountain, lake, cave or other landmark the monster of the poles The humans that live around the lake noticed that in one half of the year there isnt much fish, while in the other half of the year there is a lot. Travelers say that in the south it’s the other way around, that when there isnt much fish there, there is much in the north. So because of this people think its because of a serpent which constantly moves from pole to pole eating the fish. Others say that its because of the underworld which they believe is to be underwater, they say that the underworld is a big rock underwater that circles fast underwater causing the currents, they also think that it’s the cause of the fish disapearing. But actually its because of the seasons, in the winter its to cold for the fish to live and so they migrate to warmer spots. But most people believe it is because of the serpant because people who try swimming to look never come back.
the god among us another myth is about the mountain, which has a strong magnetic field, because of this compasses point towards the mountain. And the mountain is herefor a religious point, with temples being build on them. Many people living near the mountain believe that the mountain is a living god, which is because of the gasses it expells and of the “moving” of the mountain. They say that the god had gone to the humans to rule over them. The cave crawlers are the protectors of the god, making sure the people cant harm him. But in reality it’s massive meteorite which landed on the earth millions of years ago, the cave crawlers are spiecies that live in the caves of the meteorite, the magnetic field is because of the magnetic metals the meteorite has, and the moving of it is the mountain slowely sinking and falling, which takes a while because its stuck in the bottom of the ocean.