MSE-series was a popular line of MSE "Mouse" droids. These droids were usually programmed with a single function that varied per assignment. Once they were set on the task, they would do nothing else.
The MSE-Series General-Purpose Droid was originally sold to the Chadra-Fan homeworld. They mimicked the pleeky, a common household pet. They thought that the Galactic market would consider it "cute", and manufactured these droids in the billions. They sold very well but most of them were returned, as they reminded people of disease-carrying vermin. In one event, the entire Aar'aa species sent them back. The reason was that the little droids skittering underfoot made them uncomfortably hungry. Eventually they became so desperate that they offered every one of the droids to the Imperial Navy, as they were short on droids and needed to catch up with the other Imperial forces. They offered them for a small price and gave all of them to the Galactic Empire; every ship in the fleet had hundreds of them. Their use was only limited by their owner's creativity.
These droids were often used to carry messages in vast Imperial ships and battle stations as well as leading troops through mazes of corridors to their assigned posts. They also had two small internal arms and they could do a variety of tasks such as sanitation and security. On the Death Star, they led stormtroopers through its many hallways and levels. They were programmed to melt their processors upon capture, creating a small, localized explosion. In the Yuuzhan Vong War, some MSEs were updated to serve as miniature YVH 1 droids that specialized in detecting ooglith masquers.
The droid factories in Uffel produced a successful variant of the MSE-series, the MSF-series, at some point between 90 BBY and 53 BBY.
A mouse droid was also seen opening the door to Tyber Zann's cell on Kessel and showing a hologram of Jabba the Hutt.
An MSE-series droid.
The mouse droid has found its way into the Hasbro toy line five times to date. The 1999 fan exclusive Power of the Force 2 Freeze Frame Death Star Droid came packaged with a mouse droid. The 2002 Power of the Jedi astromech droid R4-M9 also came packaged with the same mouse droid model. The droid was released a third time as part of the 2011 San Diego Comic Con Exclusive "Revenge of the Jedi" Hasbro Toy Line Death Star set. This model was of a single piece hollow plastic mold construction with non movable wheels. More recently, it was included as a pack-in with Galen Erso in the 2017 Rogue One line and later that same year with General Hux in the first wave for The Last Jedi.
Robot Chicken: Star Wars Episode II shows the mouse droid as piloted by an actual mouse.
- LEGO Star Wars III: The Clone Wars
- LEGO Star Wars II: The Original Trilogy
- LEGO Star Wars: The Complete Saga
- Robot Chicken: Star Wars Episode II
- Star Wars: Tiny Death Star
- "Tantive IV" — Star Wars Manga: Black
- Imperial Sourcebook
- Dark Forces Official Player's Guide
- Lords of the Expanse
- Star Wars: The Visual Dictionary
- Living Force Campaign Guide
- The New Essential Guide to Droids
- "Best of StarWars.com" — Star Wars Insider 100
- The Complete Star Wars Encyclopedia
- Star Wars: Age of Rebellion Core Rulebook
- Far Horizons
- Droid Depot (toy line)