Possibility of a Big Planet Lurking out there is big, which potentially can fling some comets/asteroids into the inner solar system, most of them will be catched by Jupiters Gravity probably, but some might pass.

The Nibiru theory though seems really unlikley, unless proven otherwise. There are no real evidence atm.

Nibiru is IMHO just the biggest bullshit I've ever listened about. It is like a combination of "proofs" which are invalid, all indirect, cannot be seen and people who believe in it are already such believers that they're fooling themselves that EVERY electricity blackout is caused by it. Since I know at least basic college physics, the theory itself is interesting, but all the articles and videos trying to prove something only show how little they know about physics and that's the main reason I don't consider that theory to even be a theory.

I haven't formed an opinion yet but the NASA's [Planetary Defence Coordination Office ](https://www.nasa.gov/planetarydefense) is a fact.

There is a lot of evidence of planet X, which is now planet 9 after Pluto's status was (unfairly!) downgraded. However the whole Nibiru end of the world prophecy based on the Mayan calendar is crap.