What would happen if a rogue, Jupiter sized planet entered our solar system…?
If it crashed into one of the planets, it would destroy that planet (and probably do a lot of damage to itself). The debris from the collision could send meteors of all sizes all through the solar system, some would threaten the Earth. If it crashed into the sun, it wouldn’t do much damage to the sun, except that there would be a significant explosion/flare at the point of impact and this could cause coronal mass ejections and a wildly-disrupted solar magnetic field and wind. These could threaten the Earth. A Jupiter-sized world could enter and leave our solar system and not pass anywhere near any planets – the planets are not all on the same side of the sun, and there is a lot of space between their orbits. So its possible that it could simply pass through and not affect any of the planets at all, though it might (depending on its trajectory) disturb asteroids in the asteroid belt (and send some of them our way).
