Mari0 is a fan-made video game that combines elements of the video games Super Mario Bros and Portal. The game was developed by Maurice Guégan of Stabyourself.net, who has previously worked on parody games such as Not Tetris. Mari0 was developed with the LÖVE framework, and is cross-platform. The game was released on March 3, 2012 for Windows, Mac OS X, and Linux under a Creative Commons license (BY-NC-SA). The source code is also available to download.

The core game of Mari0 plays directly from the 8-bit Super Mario Bros. 2D platform game, where the player controls Mario via the keyboard, running and jumping through levels, avoiding or jumping on enemies to defeat them, while collecting coins to earn points towards their score. The game adds the concept of the "portal gun" from the Portal series; the player can click with the mouse device on two separate surfaces on the level to create a portal between them. This can be used for a number of gameplay options, often using vertical momentum entering one portal to "fling" the Mario character horizontally out of the other portal, but will also affect enemies and other game elements in similar manners.

The core game uses the level designs from the original Super Mario Bros. as well as sets of test chambers inspired by Portal '​s Aperture Science, but a level editor, along with different graphic sets and shaders are provided to create new content. Up to four players can cooperatively play in the game. Online multiplayer is to be released in a future version.