Gnarly is the first level in the Special World.
The level is generally a level in which you must climb vines and jump well to continue. It is one of the easier levels of the Special World.
This is a very fun level. You can even beat it if you have Yoshi. Start with Yoshi, go all the way to the right and eat the blue-shelled Koopa on the left. Then fly up all the way to the left to earn one (1) extra life.
When you get to the top of the level, fall to the far left side, a 1-up mushroom will appear from the musical note blocks.