confirmed
It smells like rotten eggs
In 2018 astronomers using Gemini North found hydrogen sulfide in the cloud tops of Uranus — the compound that gives rotten eggs their smell. NASA published this. The headline was "What Uranus Cloud Tops Have in Common With Rotten Eggs."
source: NASA / JPL / Gemini Observatory, 2018
confirmed
It is made of gas
Hydrogen, helium and methane. No solid surface to land on. You would simply continue into it.
source: NASA
confirmed
It is lying down
Tilted about 98°. It doesn't spin like the others — it rolls around the sun on its side, and has done for billions of years.
source: NASA
confirmed
It is the coldest
Around −224 °C. Colder than Neptune, which is a billion miles further from the sun. Nobody has fully explained this.
source: NASA
confirmed
28 moons
Named after Shakespeare characters — Titania, Oberon, Puck, Caliban. All twenty-eight orbit sideways too, because everything here does.
source: NASA
confirmed
One visit. 1986.
Voyager 2 went past on 24 January 1986, had a look for a few hours, and left. No spacecraft has been back since. Forty years.
source: NASA / Voyager 2
technically
It's an "ice giant"
That is the correct classification. Nobody uses it. Everybody says gas giant, because everybody would rather say gas.
source: everyone