The Super Mario X series is a 2D/2.5D sub-series similar to the New Super Mario Bros. series in the main Mario series, the games are mainly different than the regular Mario games, featuring a big story and having different gameplay in each game.
One day, Bowser decided to invade the Mushroom Kingdom again, ruining a festival called the Starlite Festival, Bowser then uses the power of 12 overpowered stars to form new worlds and send a gravity blast that effects the entire world. Mario meets Shine, a star child who helps him save the world once again.
Mario and friends go on vacation to Sunshore Isles, a tourist attraction very similar to Delfino Plaza. Things get stranger as darkness approaches - it's Bowser! Bowser doesn't want to kidnap Peach this time, but cause trouble. Black goop starts to surround the Sunshore Isles and Mario must save the way with a return of a friend, F.L.U.D.D!
Bowser is up to his evil schemes again, but his plan accidentally causes the Mushroom Kingdom inhabitants fall into it, Mario must find a way to make it to the surface. This game is very different from the previous two games and other Mario games. The game is a Metroidvania sidescroller, multiple paths to take place. Lot of unique bosses to face. Another new gameplay feature is co-op play, use two Joy Cons and play as Mario and Luigi.