Mirror Match

A Mirror Match refers to a match in which two players face off against each other using the same character.

Description
Mirror matches are often done for fun; in high-level play, it also provides the opportunity for players to discover who has the better handle on a given character, and further understand their own playstyles and that of others.

Street Fighter
While mirror matches were not technically possible in the original Street Fighter due to there being only one playable character, the two-player mode would pit Ryu against Ken, who at the time shared the same exact moveset, and played exactly the same way.

Street Fighter II series
With Street Fighter II': Champion Edition came the true advent of Mirror Matches, making it possible for players to challenge each other with the same character. In the event that a mirror match is set up and two players pick the same color character, the second player's color palette changes automatically to avoid confusion.

Street Fighter IV series
In the Street Fighter IV games, two players can now choose the same color for their character. The other character will have a tone of gray overlaying their model, making it easier to tell them apart.