WARNING: The following video is painful to anyone with either a basic grasp of science or a drop of common sense.
Now I am content to say that Nibiru actually hit the Earth on February 15, but was much smaller than had been expected, namely about the size of a house.
However, if it is indeed supposed to be more massive than Jupiter, it should be about the same diameter as Jupiter. (Oddly enough, mass doesn't have much effect on the diameter of really big planets.) This means it would become visible to the naked eye at about the orbit of Uranus. It would be easily visible to anyone with binoculars, let alone a telescope.
To be generous to how fast an unknown planet might approach Earth, imagine it was dropped from well outside the solar system and just allowed to fall toward the sun, picking up speed as it fell. By the time it reached the orbit of Uranus, it would still have about 6 years 3 months to fall before it reached Earth.
By the time it reached the orbit of Jupiter, it would be as bright as Jupiter, which is brighter than anything in the night sky other than the moon and Venus. It would be easy to see even in the largest cities. (To my great surprise, I was able to see comet Hale-Bopp from inside Tokyo. I wasn't even looking for it; I just looked up on my way home from the subway station, and there it was.) The planet would still have about 298 days to fall.
In other words, there is no way whatsoever that this could "sneak up on us".
But what if it came from the direction of the sun, like the guy in the video says?
Well, it could not have always been in the inner solar system, for a variety of reasons, ranging from the fact it would destabilize the orbits of the inner planets to the fact that it would be easy for even amateurs to see -- "presidential executive order" or not. On the other hand, if it fell from farther out and just happened to be close to the sun from our perspective right now, we would have seen it six months ago.
One more thing. The idea discussed in this first video is not exactly the same as the original idea of Zecharia Sitchin, but there are some strong similarities. Sitchin believes that a planet "Nibiru" has passed through the inner solar system before, with catastrophic consequences. In fact, he thinks it passes through the inner solar system every few thousand years, which may sound like a long time when compared with recorded human history but would still mean that either (a) a planet has just recently been bumped into an orbit that crosses the orbits of a half dozen other planets, which is unlikely, or (b) Nibiru has already passed through the inner solar system millions of times. Neither case is at all consistent with the nice, almost-circular orbits of the planets. It might be plausible if we lived in some of the wilder systems we have seen orbiting other stars, but not for our solar system.