Super Mario Underworld

Picking up right where Hack left off, Mario falls into yet another bottomless pit. At last, the players get to see the dark underworld where Mario characters travel to upon losing a life. This time, however, Mario meets up with an unexpected foe who asks a favor of him. What will Mario choose to do with this? And will he ever make it back to the Mushroom Kingdom?

While not the official final version, it contains an alternate ending. The true ending can be found here.