The N64 mouse was a peripheral for the N64.
The N64 mouse is a standard ball mouse. It has two buttons (A right click and a left click) but does not have a scroll wheel. It also has an N64 logo on the top.
The N64 mouse could be used in many of the Mario Artist games, and served as an alternative to a standard controller. It could also be used in Randnet Disk, allowing for a much smoother experience while surfing the internet.