The Star Wars franchise covers more than 40 years of actual time, and even more than that within the galaxy far, far away. It's a historic franchise and the new sequel trilogy, while trying to find a satisfying conclusion to the story, has also acted as a celebration of the franchise itself and that means that the new movies have been full of easter eggs and references to previous installments, and Star Wars: The Rise of Skywalker was certainly no exception.
One of the harder to locate easter eggs in Rise of Skywalker would have been found in Babu Frik's workshop. It's not that this was anything particularly hard to see, it's just that, once the world saw Babu Frik, it seems they could see little else, so if you became instantly obsessed with the little alien, you might not have noticed anything else in the room.
In the background of the workshop, can be found a battle droid from the prequel trilogy. It can be seen, though blurry, in the image above from the trailer for Star Wars: The Rise of Skywalker. It's clearer in the movie, as long as you notice the backgrounds and not simply the cute alien in the foreground.
Babu Frik is a black market Droidsmith, so it makes sense he would have something like an old battle droid in his possession. If nothing else, the thing is probably useful for spare parts in repairing other droids. There are probably thousands if not millions of the things left over from the various battles that took place during The Clone Wars. Although, the one on display here looks to be in pretty good shape, which is probably a rare find. Most of them likely have holes in them from Clone Trooper blasters or are cut to ribbons by lightsabers.
It's a nice addition because, in large measure the prequel trilogy doesn't get a great deal of love in the sequel trilogy. While the passion for the prequels certainly doesn't rise to the level of the original trilogy, they're still just as much Star Wars movies and should really get the same share of attention when it comes to these sorts of references.
The droid army is first seen under the control of the Trade Federation during its dispute with Naboo in The Phantom Menace, but then it becomes the main military force of the entire separatist army that is battling the Republic during The Clone Wars. We see a lot of them over the course of the animated series that takes place between episodes two and three.
Did you catch this easter egg on your first viewing of The Rise of Skywalker, or perhaps on a later viewing if you saw it more than once?