A MSE-6 droid is pictured.
MSE-series refers to a well-known series of MSE "Mouse" droids. Typically, these droids were programmed to carry out a specific task, which would depend on the assignment. Once programmed, they would focus solely on that task.
The MSE-Series General-Purpose Droid was initially marketed to the Chadra-Fan homeworld. They were designed to resemble the pleeky, which was a common pet in their households. The Chadra-Fan believed the Galactic market would perceive them as "cute," and consequently produced billions of these droids. While they initially sold well, a large number were returned due to their resemblance to disease-carrying pests. In one instance, the entire Aar'aa species returned their purchases, citing the droids' skittering movements as an uncomfortable reminder of hunger.
These droids frequently served as messengers on large Imperial ships and battle stations. They also guided troops through labyrinthine corridors to their designated locations. Equipped with two small internal arms, they could perform tasks such as sanitation and security. On the Death Star, they guided stormtroopers through its extensive network of hallways and levels. Upon capture, they were programmed to self-destruct, creating a small explosion. During the Yuuzhan Vong War, some MSEs were upgraded to function as miniature YVH 1 droids, specializing in the detection of ooglith masquers.
Sometime between 90 BBY and 53 BBY, the droid factories located in Uffel successfully produced a variant of the MSE-series known as the MSF-series.
Additionally, a mouse droid was observed opening the door to Tyber Zann's cell on Kessel and presenting a hologram of Jabba the Hutt.
The mouse droid has been included in the Hasbro toy line on five separate occasions. The 1999 fan exclusive Power of the Force 2 Freeze Frame Death Star Droid was packaged alongside a mouse droid. The 2002 Power of the Jedi astromech droid R4-M9 was also packaged with the same mouse droid model. A third release occurred in 2011 as part of the San Diego Comic Con Exclusive "Revenge of the Jedi" Hasbro Toy Line Death Star set. This particular model featured a single-piece hollow plastic mold construction with wheels that could not move. More recently, it was included as a pack-in item with Galen Erso in the 2017 Rogue One toy series and later that same year with General Hux in the initial wave for The Last Jedi.
In Robot Chicken: Star Wars Episode II, the mouse droid is depicted as being piloted by an actual mouse.