Warning: This piece contains a very minor spoiler for Rogue One and how it affects the larger Star Wars mythos.
During the season one finale of Star Wars Rebels, Kanan is captured by the Grand Inquisitor and taken to Mustafar. Hera says to the crew of the Ghost, “I’ve only heard that name once, from Kanan. He said Mustafar is where Jedi go to die.”
Fans heard that line and immediately thought of Episode III, and while it’s entirely possible to legend of what happened to Anakin Skywalker could’ve reached Kanan over the years; the line has new meaning following a small revelation in Rogue One.
Mustafar is where Vader’s castle is located in Star Wars canon. It’s a change from the location in Legends, and it opens up a very cool idea for the planet and its place during the Empire and Rebellion era.
“Where Jedi go to die” could mean literally that. With Vader living on Mustafar it’s not the place an Order 66 survivor would want to stumble upon. Even bigger, it explains why Inquisitors would bring Jedi to the planet.
In Rebels we never got down to the surface of Mustafar, the entire finale took place in orbit on Star Destroyers. What would’ve happened to Kanan if the Inquisitor brought him down to the surface? It’s likely he would’ve been brought face to face with Vader.
What Vader would do to Jedi on the planet is something that hopefully will be expanded upon via books, comics, or even Rebels in the future. Perhaps he’d give them the chance of turning to the Dark Side, only killing them on the same planet where he was created if they resist him.
Mustafar as Vader’s home also makes a lot of sense. It’s where he was betrayed, where he was left for dead, and where he killed his wife. There’s a lot of anger for him to feed off there, and putting his castle on that planet in canon is pretty brilliant. It’s one of the coolest Prequel references in Rogue One, and it really opens up some incredible storytelling possibilities for Vader in the future.