A Light in the Dark

This level is Yoshi's Island DS's answer to Super Mario World's Tubular. This is by far the most difficult level in the game, even moreso than Yoshi's Island Easter Eggs. In this level, you start out in a castle where your goal is to find two keys to unlock two doors. It's extremely easy to lose a life here due to all of the spikes and purple skies throughout the level. The entire level is lit by torches. Once you get the keys, you then go outside onto a mountaintop at night illuminated by torches. You then have to complete a skiing section which involves instantaneous decisions and perfect timing. This is a section where most players lose up to 50 lives. Once you complete that, you must get past a small maze section with spikes throughout populated by crabs. There is a small Superstar Mario section right before the goal followed by use of the smiling platforms which are affected by you standing on them.