Super Mario Bros. X
Probably the most faithful re-creation of the classic Mario style, Super Mario Bros. X serves as a general-purpose engine for anybody wishing to create a set of Mario levels and some custom gimmicks. It is in many ways an unofficial precursor to Super Mario Maker.
Mario physics and gameplay are replicated with meticulous detail and there’s even some awesome additions, such as the ability to play as Link. I do feel, however, that the included map packs are somewhat lacking. For the most fun, I recommend downloading one of the many 3rd party sets on offer: these range from conversions of classic Mario games to crazy and absurd endurance runs.
Warp on over to the official page to make it part of your collection.