Hold II and press Run at the difficulty selection menu.
Enable the "Bonus round practice" code, highlight
the "Exit" option, then press II + Run.
Press Run to pause game play, then press I + II + Select.
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.