There is no such thing as “Planet X”. I think this story got started with some old science fiction tale, with the fictional idea being that there is an earth-sized planet in orbit in the same orbit and with the same revolution rate as the earth but on the opposite side of the sun, so that we can never see it. However, any space agency would have seen it by now if it existed, and any astronomer who is good with math could calculate perturbations of the orbits of Mercury and Venus and detect a mass on the opposite side of the sun as the earth. In fact, astronomers several hundred years ago could have detected this if it existed.

What is far more of a reality is guys on the internet making up science fiction and calling it “real” and making up as many disaster stories as they can. They seem to be competing with each other to make up the most outrageous types of stories.