Super Mario Land 2: 6 Golden Coins (GB)
In a level that you've already finished, press Start to pause and then press Select to quit the level.
On the Title screen, press Start to enter the file select screen. In this room, press Select to enable "Easy Mode." You can then begin any saved file you wish.
Play the demos
Note: This will not work on the "Players Choice Million Seller" edition.
When the title screen appears, hold one of the button combinations below (until the screen changes) to play in a demo. After playing the demo for about 60 seconds, the game will freeze and you'll need to reset.