& is a CPU Mii. Pronounced as the word and.

What & most likely looks like.
Wii Sports[]
Much about & is unknown, but in Baseball his level is 1,012,000. He plays with Shouta in Tennis.
Wii Sports Resort[]
In Swordplay his level is 5216.
In Basketball his level is 3837 and plays with Merome and Misami.
In Table Tennis his level is 26172.
Wii Party[]
In Wii Party, & is an Advanced Master CPU.