Hold II and press Run at the difficulty selection menu.
Get the blue heart in the first level in round 2
There is a blue heart on top near the bamboo tree. Go on the bouncy thing which leads up to the three bricks. Go on the top brick, then to the brick with the horns on it. Then, jump up on top of the thorn brick, and there you are. Keep walking across it, and you will get some happy faces along the way. Then, jump down and you will get the blue heart.
Preview ending sequence
Enable the "Bonus round practice" code, highlight the "Exit" option, then press II + Run.
Remove "Pause" text
Press Run to pause game play, then press I + II + Select.