Mario's Picross/Secrets

Super Game Boy border colours
When playing the game on a Super Game Boy, the border is identical to the upper half of a Game Boy handheld. After pressing or  on the title screen, the border will change colours from a gray Game Boy to a green one before the screen fades to white. By entering a code or holding a direction on the control pad, you can have the border change to one of five different colours.

Transparent
On the title screen, press and release, , , and. The order in which you press the directions does not matter. After hearing a "confirm" sound, press or  to continue and the border will change to a transparent Game Boy.

Pressing a direction after the sound will deactivate the code, but it can be reactivated by pressing the same direction again. This works because the game toggles a flag in memory on or off whenever a direction is pressed and the code activates when all four flags are on.

Yellow, red, black, or white
Before the border changes colours, hold down one of the directions on the control pad. The direction you hold will determine the border colour.

This can be done either before or after you press or  to proceed from the title screen.

The game processes the directions in the same order as the above table and the transparent border takes priority over these colours. Thus, if multiple directions are held, you will receive the colour that is closest to the top of the list. If the transparent border code is activated and a direction is held, then the colour will still be transparent.

Star Picross course
Complete all of the puzzles in the Kinoko course to unlock the Star course in Picross mode.

Time Trial mode
Complete all of the puzzles in the Kinoko and Star courses to unlock the Time Trial mode in Picross mode.