Super Mario 256
Super Mario 256 is a mod based on Super Mario 64 DS that has new levels, enemies, power-ups, and more. From the flowery scenery of Yoshi’s Beautiful Garden to the crystalline depths of Underground Shell Cave, this mod has levels with a variety of settings. The Stumplets of Flip-Jump Swap-Kick Woods are just one of the new varieties of enemies, and some veteran Mario enemies such as regular Shy Guys also show up where they didn’t in Super Mario 64 DS. The Bee Mushrom and Cloud Flower from Super Mario Galaxy 2 also appear, but expect all-new power-ups as well.
A demo is available here. Note that it requires patching with a Super Mario 64 DS ROM. Also note that saves don’t work properly on MelonDS; you should use savestates if you use that emulator.