Mario DOS Madness is a fan-made concept, likely referencing the older DOS operating system and implying a retro style. Its gameplay would probably be a 2D or pseudo-3D platformer with limitations in graphics that resemble DOS-era games.  It would likely draw inspiration from the Super Mario series but adapt it for the retro technical limitations.  The creators would be indie developers or ROM hackers aiming for a nostalgic and unique approach. 

Mario DOS Madness

Mario 64 Seasons