I wonder about a Planet Nine having a close encounter with Earth at some point, or at several points.
This particular candidate never gets closer to the Sun than 400 A.U., Earth’s distance from the Sun is 1 A.U. :^) In short, probably not.
The same thought occurred to me --- if there is a planet, its orbit is important.
There are comets out there with elongated, eccentric orbits that take them far outside the solar system, such that it takes decades or even centuries to complete a single orbit. It's only when they approach the sun that they become visible. One of them collided with Jupiter last year, as I recall.
What if there's a planet out there whose orbit crosses ours? Could be trouble.