If you're pining for some classic Mario and don't have a copy of Super Mario Maker to hand, there's always Newer Super Mario Bros. DS. As the name implies, it's a fan-made successor to the portable title from 2006. The 80-level campaign was created with the free and legally dubious New Super Mario Bros. Editor, and requires a ROM of the original DS game to run. If you can find one and a compatible emulator (the team says it works "pretty much perfectly" with DeSmuME) you can play the game for free.
The stages stretch across eight world maps, with "new and updated game mechanics," a fresh soundtrack and "the return of a classic power-up." Nintendo is a stickler for copyright infringement, so there's a good chance the game will disappear in a week or so. The creators of the project, however, also made Newer Super Mario Bros. Wii, which is still available to download. So who knows, maybe this one will escape the big N's legal clutches? For more fan-made Mario goodness, we recommend this head-spinning hack that turns Super Mario 64 into a first-person adventure.