Adventure

Start a game then press SELECT to get the game selection screen (with the number in the center). Pull down and Hero will appear. (You can't do anything but move around the screen however.)

Hit SELECT as soon as you finish and you'll hear the ending fanfare play really slow.

Placing the bridge at the bottom of the screen and crossing it (off the screen) will sometimes get you "stuck" on top of a castle.

On game two or three, go to the maze in the Black Castle. One screen left of the first maze screen will flicker if you carry an object in there meaning one thing, there's ANOTHER object in there. At the bottom center of this room is a closed off cubicle, use the bridge to get in there and you should pick up a "dot". Carry this to the screen just above the catacombs (one screen down and to the right of the Gold Castle) and be careful not to lose it as it's the same color as the outside ground. Drop it there and bring two other items onto the screen, run right through the line on the right side of the screen and witness the first ever Easter Egg.