Physical Appearance:
* Tiny: Emphasizing small size
* Gray: A common color
* Brown: Another common color
* White: Describing a white mouse
* Black: Describing a black mouse
* Sleek: Describing a smooth, well-groomed mouse
* Scrawny: Describing a thin, underfed mouse
* Plump: Describing a fat, well-fed mouse
* Furry: Describing the texture of its coat
* Long-tailed: Emphasis on the length of its tail
* Squeaky: Describing the sound it makes
Behavior:
* Shy: Describing its cautious nature
* Timid: Describing its fearfulness
* Curious: Describing its inquisitive nature
* Nimble: Describing its agility
* Agile: Describing its ability to move quickly and easily
* Stealthy: Describing its ability to move quietly
* Cunning: Describing its intelligence and ability to outsmart others
* Destructive: Describing its tendency to chew on things
* Pesky: Describing its annoyance
* Noxious: Describing its ability to spread disease
Other:
* Cute: Describing its appearance as adorable
* Domesticated: Describing a mouse kept as a pet
* Wild: Describing a mouse living in the wild
* Field: Describing a mouse found in a field
* House: Describing a mouse found in a house
You can also use descriptive phrases:
* A tiny, gray mouse with a long tail
* A plump, brown mouse with beady eyes
* A stealthy, cunning mouse that scurries through the shadows
The best adjectives to use will depend on the specific context and the effect you are trying to achieve.