Fire rats were a type of creature native to Mustafar. They were known to gnaw on the lava crystals that could be found on the volcanic world. While recounting a tale to the prisoner Thom Hudd about the exploits of the droid captain Spikewheel and her crew on Lotho Minor, the Sith attendant Vaneé likened the fear gnawing at the group to the teeth of fire rats gnawing at crystals.
Fire rats were first mentioned in Star Wars Adventures: Return to Vader's Castle 1, a comic issue written by Cavan Scott and published by IDW Publishing on October 2, 2019.