Serolonis, alternatively spelled Serralonis, was a planet of the desert type, situated within the galaxy. It gained notoriety due to the Riot Racing sport it hosted, with competitions occurring at the Safa Toma Speedway located on Safa Toma, where spectators engaged in wagering.
Between the years of 19 BBY and 18 BBY, the formed Galactic Empire did not exert control over it. During this time, Clone Force 99 members Tech, Wrecker, and Omega journeyed to the planet aboard a Star Commuter 2000, along with information broker Ciddarin Scaleback, to rendezvous with Cid's droid racer, TAY-0. Subsequently, Cid placed a wager with Dowutin crime lord Grini Millegi, betting that TAY-0 would emerge victorious in the upcoming race. However, Nosaurian racer Jet Venim secured the win. Unable to fulfill the bet, the Bad Batch members intervened, proposing a new agreement: they would pay double if they were to lose the subsequent race. With TAY-0 out of the picture, Tech took on the role of racer for Cid and won the race, thus rescuing Cid from Millegi's grasp.
Kullbee Sperado's location was Serolonis when Saw Gerrera enlisted him to become a member of the Partisans.
Serolonis was a planet characterized by its desert landscape, primarily consisting of sand dunes and rugged terrain. From a vantage point in space, it presented as a reddish-yellow sphere interspersed with patches of green. The planet featured at least one settlement, with the Safa Toma Speedway serving as its main attraction, a venue where spectators gathered to witness Riot Racing, a popular sport on the planet. By 18 BBY, the world had become a haven for various outlaws, smugglers, and gamblers.
Serolonis made its debut in the Star Wars: The Bad Batch episode titled "Faster." The planet derives its name from the esteemed Italian director Sergio Leone. Initially, it was conceived for an unfinished arc within Star Wars: The Clone Wars, featuring Cad Bane and a young Boba Fett. While the trivia gallery for the episode on StarWars.com spells the planet's name as "Serolonis," the concept art gallery for the same episode displays the name as "Seralonis." The planet was first referenced as "Serralonis" within the 2016 reference book, Star Wars: Rogue One: The Ultimate Visual Guide, in relation to information about the character Kullbee Sperado. However, it wasn't until the 2024 reference book, Star Wars Encyclopedia: The Comprehensive Guide to the Star Wars Galaxy, that "Serralonis" was confirmed to be the same location as Serolonis, as its entry for Sperado adopted the Serolonis spelling.