Super Mario Bros. X is a Mario fangame that blends elements from Super Mario 1, 2, 3 and World. It has many power ups, such as the Ice Flower, Hammer Suit, Tanooki Suit, Kuribo's shoe, The Billy Gun, and Yoshi. You can also play the game with a friend in the 2 player co-op mode, where the screen seamlessly splits and combines as the players separate and rejoin. This fangame is most notable for its extensive level editor that allows you to create almost any kind of level that you can imagine.

The game and engine were supported by the original creator until 2011.