No, that isn't Mario transported into The Legend of Zelda: Majora's Mask. The world of Majora's Mask has been inserted into Super Mario 64.
YouTuber and modder Skelux recreated the entire Majora's Mask world (minus the dungeons) in a single level of Super Mario 64. Watching Mario run around Clock Town and the rest of the dark, scary world of Majora's Mask is pretty incredible, albeit unsettling.
This isn't Skelux's first Mario/Zelda mash-up. In September, they remade the entire Ocarina of Time overworld in Super Mario 64.
If Skelux is going to keep modding 3D Zelda games into Super Mario 64, Wind Waker would have to be next. That would be a very impressive feat.
