2020 Update: Since February 2, 2020, the source code of SMBX is now open under MIT license (license file in a repository): Here is a news post about that: SMBX Legacy Source Code Latest Bulletin Currently, there is no stane-alone option for distribution. Levels and episodes made in SMBX require the engine to play. Besides Mario and Luigi, there are also Toad, Princess Peach and Link as playable characters. There are classic power-ups such as the Fire Flower, Tanooki Suit, Yoshi, and Kuribo's Shoe, but also new power-ups like the Ice Flower, The Billy Gun, and the Propeller Block. Custom graphics and custom music can be imported into levels. The game is playable with a friend in the 2 player co-op mode, where the screen seamlessly splits and combines as the players separate and rejoin.

It is possible to create episodes using either the SMB3 or SMW styled world map, or using a Mario 64 style hub level that has the players collect stars to advance. It contains an extensive point-and-click level editor that allows for the creation classic Super Mario Bros. engine project that blends elements from Super Mario 1, 2, 3 and World, with SMB3 physics.

Smbx 1.4.4 .map