The Mirror Match is a special match battle introduced in Mortal Kombat. The player has to face the character that they're playing as in kombat. The difference between each identical character is distinguished by their clothes.
In the original Mortal Kombat tournament, kombatants had to not only face their enemies in battle, but themselves. Facing a doppelganger, players had to defeat a warrior who shared their own strengths and weaknesses. Essentially, it is a duel where one must overcome themselves if they are to face the likes of Shang Tsung as they become truly aware of their own strengths as well as the weaknesses they can conquer.
In Mortal Kombat X, mirror matches are a topic of interest thanks to the unique interactions that each kombatant has before a fight. In one instance with Reptile, his double is Shang Tsung himself when Reptile assumed he was Chameleon. Other instances heavily imply the convergence of different timelines as Raiden must fight against an alternate version of himself who fights for Chaosrealm instead of Earthrealm while the Scorpion of the new timeline is faced against his original counterpart during his time as the Elder Gods' champion, with Lt. Sonya Blade meeting her future Gen. Sonya Blade self. Also, Shinnok faces his double who [he] "didn't kill at the pyramid".
This level of intrigue would later return to play a big role in the story of Mortal Kombat 11 where characters are be faced with past versions of themselves, particularly Liu Kang and Kung Lao confronting their future Revenant counterparts. In one Mirror Match, the Scorpion from Mortal Kombat X is seen acknowledging and defending Kuai Liang's sincerity in their newfound alliance while the opposing version believes Sub-Zero to be treacherous. In other cases, characters are faced with family members with identical visages such as Bi-Han in his human form, Liu Kang's ancestor Cheh Kang or Shang Tsung's brother, Shang Lao. Interactions between future and past selves also come with immense risks as damage inflicted on the past self will be reflected on the future self such as the younger Johnny Cage being shot in the face with the exact same scar being reflected on the older version as well as feeling their pain.