It is harder than the original Super Mario Bros, with fewer warp zones and power-ups, and more enemies. Some of the courses were even taken from the sequel, Super Mario Bros. The Lost Levels.
Downloads:
Mari0 1.6: ZIP RAR
Alesan99's Entities Version: ZIP RAR
SE Version [Unfinished]: ZIP RAR Windows Users: If you download with rar, You need WinRAR or 7 zip.
Credits: FuriousHedgehog for fixing my alesan99 version of the mappack.
Alesan99 for the mod.