Fact: None of the outer dwarf planets orbit any closer to the sun than the inner limit of the Kuiper Belt (the gray zone in the drawing below. All the normal planets [Mercury to Neptune] are closer to the sun than that zone of 30 to 55AU.). If any outer planet orbited closer to the sun than 30AU then it would either crash into a planet or would be thrown off course by the gravitational force of Jupiter or Saturn. There may have been other planets that did that before and were either destroyed or redirected off into space never to come back again. In the black background graphic you can see the orbital paths of the known outer planets. The one that gets the closest to the sun is TG422 at 35.6AU. (1AU is the distance from the sun to Earth.)
Below you can see to scale the distances of the inner planets to the sun. Earth is very far from the Kuiper Belt and is basically protected by Jupiter since any large planet that comes near would be thrown off course by the gravity from Jupiter and would lose its normal orbit and so would never come back again. All the outer planets are dwarf planets (smaller than Pluto) except for the proposed Planet Nine which doesn't get any where near the orbits of the inner planets.
The originator of the idea of a passing planet dangerous to life on Earth was by a New Ager whose predictions have not come to pass. The idea of a dangerous passing planet was first put forward in 1995 by Nancy Lieder, founder of the website ZetaTalk. Lieder describes herself as a contactee with the ability to receive messages from extraterrestrials from the Zeta Reticuli star system through an implant in her brain. She states that she was chosen to warn mankind that the object would sweep through the inner Solar System in May 2003 (though that date was later postponed) causing Earth to undergo a physical pole shift that would destroy most of humanity. The prediction has subsequently spread beyond Lieder's website and has been embraced by numerous Internet doomsday groups, most of which linked the event to the 2012 phenomenon. Since 2012, the cataclysm idea has frequently reappeared in the popular media; usually linked to newsmaking astronomical objects such as Comet ISON or Planet Nine. [source]
Zecharia Sitchin, author of the belief in a planet inhabited by aliens called Nibiru has been debunked. see https://www.youtube.com/watch?v=aiMOy4oVi7s
He promoted the idea that aliens called Anunnaki (from Nibiru, which he says are also called Nephilim in the bible although the bible said they were born of human women, not aliens) had been here although looking up the word indicates he hijacked it for the purpose of embellishing his new fable. https://en.wikipedia.org/wiki/Anunnaki says "The Anunnaki are a group of deities [gods] in ancient Mesopotamian cultures (e.g. Sumerian, Akkadian, Assyrian, and Babylonian). According to The Oxford Companion to World Mythology, the Anunnaki: "...are the Sumerian deities of the old primordial line; they are chthonic deities of fertility, associated eventually with the underworld, where they became judges. They take their name from the old sky god An (Anu)." The Wikipedia page on Sitchin states the main errors that he has made which means he just created a story for fame and profit: https://en.wikipedia.org/wiki/Zecharia_Sitchin If humans advanced intelligence is the result of genetic manipulation by aliens then it certainly wasn't by the "Anunnaki from Nibiru".
Planet Nine has yet to be verified. As of now it is just a theory that if true would explain certain changes in planetary orbits of dwarf planets in our outer solar system. But the calculations for its orbit do not agree with the Nibiru believers idea that it comes to the inner part of our solar system where it can wreak havoc on Earth. The calculations predict its path to come not within the interior of our solar system but rather only to within 200 Earth-to-Sun distances (200AU) which is nowhere close enough to wreak any havoc on Earth. [source] And if you think that it can cause problems at 200AU from the sun then consider this; Jupiter has a mass that is 317 times that of Earth and it comes to within 4AU of Earth at its closest. The force of gravity is calculated by the two masses of the attracting objects multiplied together divided by the square of their distance. So if Planet Nine has 4 times the mass of Earth and it gets to be 199AU from Earth then the gravitational force between the two is 1/196000 that of the force between Earth and Jupiter. So if Jupiter-to-Earth has a force of 1 then Earth-to-"Nibiru" has a force of .000005 which is next to nothing in comparison.
Everyone saying they see Planet Nine (aka Nibiru) are just full of crap. For example, photos of a secondary sun-like source of light can only be a visual lenses error of the camera or a UFO. It can't be a planet because planets don't shine light, they only lightly reflect light. The weather anomalies we are having now aren't due to a rogue planet close to us but rather to a combination of global warming and the grand solar minimum which happens every 400 years or so. Look it up.
I'm so tird of idiots cluttering up youtube with astronomical "fake news". I wish youtube would ban them. If you believe in an end-of-world scenario caused by Nibiru then:
1) you are just ignorant of the facts I just presented. (but now you know the facts so you have no excuse)
2) you're neurotic and emotionally synchronize with all news that is traumatic.
3) you promote the idea on youtube videos just for the popularity and notoriety it brings you.
4) you are an illogical person who can't be persuaded with facts. (probably a religious person or New-Ager)