Debug Menu:

Power on the console and wait until the demo starts. Press A to skip it, then wait for it to play again. Skip the demo a total of four times. After the fourth time, wait until the title screen appears, and then wait until a blinking animation follows the titles name from left to right. Press the A Button exactly when the blinking begins, but before it passes the "T" letter in the name. If done properly, the debug menu appears.

 

Secret Ending:

If you wait for an hour after beating the game, just sitting there at the ending animation screen, you'll find a new animation and a hidden message from the developers.