VB Mario Land is a prototype of the Mario Virtual Boy game that actually became Mario Clash. Nintendo was originally developing this as a full mario platform game, as show at E3 1995. The original project was cut and Mario Clash became just a remake of the classic Super Mario Bros, with featured small 3-d elements to show what the Virtual Boy was graphically capable of. For example, some parts exchanged the original idea of warp pipes with 3-d doorways that players enter by pressing up on the D-pad.
You can find more infos at Planet Virtual Boy