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.
Using Yoshi, you can also get up to 7 Dragon Coins (it is generally impossible to get more than 5 in a level). Grab the blue-shelled Koopa, fly up to the hidden P-Switch (hidden in a yellow block near the first red Koopa Para-Troopa) making sure to skip the first Dragon Coin you see but get the second, discard but do not kill the blue shell, grab the P-Switch, take it to the very top of the middle divider and drop it there, fall down the right side of the divider while collecting three more Dragon Coins (for a total of 4), re-grab the blue-shelled Koopa, fly up to the P-Switch you left earlier, stomp it, and then fall part way down the right side again to the pipe you can now enter. You will find 3 more Dragon Coins, and 3 1-Up mushrooms. The 3 extra Dragon Coins do not appear if you got all 5 in the previous area.
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.