The Rise of Skywalker begins with quite a bit of Dark Side action. We see Kylo Ren taking down some mystery aliens on an unknown planet with a Stormtrooper escort. This has been shown in a lot of promotional footage for the sequel and is also included in an extended clip that was released over a week ago now, so there's no spoilers yet. However, we're never told where Kylo Ren is and who he's taking down in the footage. Thankfully, we now have the answer. There are SPOILERS for The Rise of Skywalker below, so read ahead at your own risk.
As it turns out, The Rise of Skywalker begins on Mustafar, which all Star Wars fans will more than likely recognize as the place where Anakin Skywalker and Obi-Wan Kenobi had their fateful battle and where Skywalker, as Darth Vader, builds his castle. The new sequel reveal is detailed in Star Wars: The Rise of Skywalker: The Visual Dictionary. Author Pablo Hidalgo has given us some information as to why Kylo Ren is there in the first place. You can read an excerpt from the book below.
"Kylo soon outpaces his stormtrooper escorts as he cuts a swath of destruction through the Alazmec who attempt to block his path to Vader's castle - or rather, its crumbling ruins. Kylo enters the castle grounds with purpose, and finds an ark containing an artifact that will lead him to answers."
As for who the Alazmec are, they're the unfortunate aliens who Kylo Ren is easily mowing down with his Lightsaber at the beginning of the movie. They're described as "cult colonists" who "voyage to Mustafar in pilgrimage seeking to tap into the powers that supposedly fueled him," and wear "sodium silicate-dusted protective clothing." They also wear some pretty large goggles to protect their eyes from all of the ash. While one doesn't necessarily think of trees on Mustafar, the book says the "thin forest of irontrees" were planted "in a futile attempt to reinvigorate the glen that covered the land centuries earlier."
There's unanswered questions in The Rise of Skywalker and going to Mustafar is pretty huge for Star Wars fans. It's something that could have easily been addressed in the opening crawl and something people would probably have been happy about. Seeing Kylo Ren on the planet where Darth Vader's crumbling castle resides is a big deal, but at least Pablo Hidalgo has our backs. One can imagine that Star Wars: The Rise of Skywalker: The Visual Dictionary is extra thick to explain everything that was left out of the movie.
Also, getting ahold of the "artifact that will lead him to answers," makes a lot more sense knowing that it was located on Mustafar. From there, Kylo Ren goes straight to Exegol to meet with Emperor Palpatine. It's a dark scene and we are treated to even more knowledge about the sequel trilogy, including the long-awaited Snoke reveal. You can head over to The Official StarWars.com website for purchasing information on Star Wars: The Rise of Skywalker: The Visual Dictionary.