New Super Mario Bros./World 2-A

A lake in the middle of the desert would usually be a blessing, but this particular oasis is inhabited by a nasty creature called the Spike Bass. This monstrous fish will relentlessly attack you, and the only way to be safe is to stay above of its leaps. Spin Blocks make a return, use them wisely to remain in the sky.

Level walkthrough
Upon entering the stage, you'll immediately notice a layer of water covering the lower part of the screen. There is a single but very prominent threat that lives in this lake, the Spike Bass. This huge fish can't be defeated by stomps, so you need to resort to using fireballs or shells. Even if you do knock it out, it will soon return and resume its assault. Look out for platforms around the height of the first hill you come across, as the Spike Bass's jump can't reach you on these spots. Go forward and you will spot several Koopa Paratroopas, then a red Koopa Troopa later on. You can hold on to their shells in case you need to temporarily take out Spike Bass. There is a Star Coin to the right of the red Koopa, but it is dangerously close to the water. You can use a Koopa shell to collect it safely.

After the first Star Coin is a stretch of water without any safe land. You must use the nearby Spin Blocks to spring up high into the sky, completely evading the Spike Bass's attacks. Follow the trail of coins in the air to the next Spin Block, letting you jump further on to a small island at the middle of the oasis. On the island, spring off the next Spin Block and drift to the right to land on a block high above the ground. Jump a bit to the left to reveal hidden coin block, then jump directly up from the hidden block to hit a hidden 1-Up block. Jump to the left to step on a series of blocks, passing by the checkpoint on the way.

At the end of the blocks, jump straight down past some coin outlines to land on another Spin Block. Spring up and follow more coin outlines to the next Spin Block. Continue drifting to the right, carefully avoiding the red Koopa Paratroopas. Keep an eye out for the final Spin Block, which lets you reach a bunch of tall platforms, as well as help you collect the second Star Coin, which is hanging openly in the air. You will soon reach the end of the stage. Go down the green warp pipe to enter the area with the flagpole. Use the Spin Block here to spin up high, then try to land on the red Koopa Paratroopa to propel yourself up some more, using the increased height to touch the top of the flagpole.

Once you clear the stage, you will be able to access a Warp Pipe on the overworld, which takes you straight to the castle, a pretty big shortcut.

Star Coins

 * 1) Above the water a bit to the right after the first red Koopa.
 * 2) Suspended midair below a platform near the end. Drift to the coin slowly after jumping from a Spin Block.
 * 3) Right in your path when going down the path to the red flagpole.

Alternate exit
Above the green Warp Pipe that takes you out of the oasis is an alcove with the yellow Warp Pipe. After you jump up from the last Spin Block, drift right and attempt to land on the red Koopa Paratroopa, which will bounce you up to the yellow pipe. Go through it to reach a blocked-off section of the original flagpole area, where you can obtain the third Star Coin. Go down the red pipe to be taken to the red flagpole. Jump to the right of the two blocks to hit two more hidden blocks, which will help you jump to the top of the flagpole.

The secret exit leads to the World 2 Cannon instead. This cannon sends you to World 5. The extreme change in climate isn't the only big difference between the two worlds, and the increase in difficulty can be hard to overcome.