The oceanic Kamino planet from Star Wars could mostly exist except for its constant raging storm. The Mustafar lava world is the imagination gone too far off the scientific rails.
The story of the Kamino planet is that it’s inhabited by Kaminoans, shown above, a sentient species that established an advanced technological civilization when their planet still had continents, but the end of a long ice age caused the landmasses to be flooded, and the Kamino became an ocean world. Kaminoans then built cities on stilts that rise above the water.
This is mostly plausible. One of the most difficult aspects of planets like Earth is the fine line between the amount of water they have. A little too much, and it could be a global ocean planet. Earth might initially have had only one continent rising above the water when plate tectonics began. It’s not difficult to imagine a world where this fine line between the amounts of water needed to cover all landmasses is narrower, and an ice age could trap this much at the poles, causing the continents to be revealed and flooded after a change in climate and the end of the ice age.
It’s more difficult, though, to accept that there would be a raging, constant storm with heavy rainfall. A planet without landmasses, with a nearby large moon and a thicker atmosphere, could indeed have had stronger winds and more precipitation. Fast spinning could make storms more severe, but there would need to be some calmer days.
The Mustafar is just outright not plausible. In Star Wars lore, it's described as a volcanic world orbiting between two gas giants, which causes intense volcanic activity. I don’t see it working this way. Such a planet wouldn’t be stable. It would make more sense if Mustafar were a moon of a huge gas giant, and intense tidal effects would cause the bending of its crust and volcanism similar to that of Io, Jupiter's moon.
However, in Star Wars, Mustafar has a breathable atmosphere and is inhabited by advanced organisms, including a bug-like sentient species. Where do they get oxygen to breathe from, since the planet is a lava world without any water, oceans, or forests where photosynthetic organisms could produce oxygen? The only workable solution would be if this lava environment were located on a large continent surrounded by a global water ocean, but even then, we run into problems with the volcanism and magma being just too intense for a water ocean to be plausible alongside it.
Therefore, Mustafar is the author's imagination going too far to make it plausible.