Hudson's Adventure Island

Continue game play:

Locate the hidden egg at the end of level 1. It can be located by jumping directly upward at the edge of the cliff just before the "G" sign. Smash the egg and collect the Hudson bee logo. Hold Up + A + Select and pressStart at the game over screen to continue game play at the start of the last level played. Alternatively, hold Right and press Start to continue game play.

Island select:
Allow the game to reach the title screen, then reset the NES console. Then, press Right, Left, Right, Left, A, B, A, B when the title screen appears again. Alternatively, press Down, Up, Left, Right, B, A, B, A at the title screen.

View next Boss:
Kill the first Boss and pause game play as he leaves the screen.

1000 point bonus:
Locate the red flower in level 1-4. Shoot the coyote that attacks from behind twice while jumping to display a power-up in the form of a Nintendo controller. Get the controller to collect 1000 points.

Bonus level:
Get to the middle of level 1 where some kind of wooden voodoo objects are located. Just after the fire appears in the middle of the two voodoo objects, shoot about ten times (even if do not have a weapon). You will see something that will get you to a bonus level. 

출처 : http://www.gamewinners.com/nes/AdventureIsland.htm