During the intro sequence, hold the Down + Right + A buttons once you see the chests on screen all the way until the music stops playing when you reach the title screen.
You can skip the rock, paper, and scissors sequences against bosses by pressing Start (to enter the Options menu) after you conversation with the boss in question ends. Then simply press Start again to exit, which will also allow you to skip the minigame.
To do this, simply press Start and press an item for approximately one minute.
Before starting a game, go to the options menu. With the curser on continue, press start on the controller. You will now get unlimited lives.