Mystique was originally introduced into the Marvel comics as a villain and enemy of the X-Men in the 1980's. She was later introduced into the gaming franchise and made her first appearance in the arcade game X-Men in 1994.
Mystique made her first ever appearance in the arcade version of X-Men, where she appears disguised as Professor Xavier between Stage 5 and 6. She is the main boss in Stage 7, Asteroid M, in which she takes the guise of Magneto and attacks the player with various martial arts.
X-Men: Mutant Academy
Mystique is an unlockable character in the first installment of the fighting game X-Men: Mutant Academy. She also appears in the sequel X-Men: Mutant Academy 2 where she wields a large gun. Her combo moves consist of a range of punches and kicks coupled with gunshots.
X-Men: Next Dimension
Mystique is a playable character in X-Men: Next Dimension and is one of the first bosses the player faces if they choose Forge as their character.
Mystique is the first boss the player faces as Wolverine in the beginning of the game and can be unlocked for the player to use in Training Mode. She returns in the sequel, X-Men: Legends 2, as a non-playable character and has special dialogue with Rogue of the X-Men.
Marvel: Ultimate Alliance
Mystique is mentioned in the ending, should the player choose to save Jean Grey from being dropped in the Infinity Vortex in Mephisto's Realm. She avenges her son, Nightcrawler, by taking her frustration out on Professor Xavier, which results in the X-Men disbanding.