How to clear Valley of Bowser 2 in Super Mario World for the Super Nintendo Entertainment System and Game Boy Advance.

How to Complete Valley of Bowser 2
Go to the right and jump onto the rising and falling Sand Tide, but beware of the Swooper that swoops down from the ceiling above. As you go through this area, Swoopers will fly down from the ceiling, so watch out.
Go to the right and there are five coins with a green Koopa Troopa between. Farther ahead, there is a green Koopa Troopa beneath a Prize Block. As you approach the Prize Block, be careful of the Flashing Shell that spins into this area from the right. You can destroy it with a Spin Jump or have Yoshi eat it if you have Yoshi (which gives him the abilities of all three shells, i.e. flying, creating sand clouds when he lands on the ground, and spitting flames instead of spitting out the shell). The Prize Block contains a Cape Feather.
After that, you can get a total of six coins, and you will encounter two green Koopa Troopas. After that, go down to the lower area, where there is another green Koopa Troopa, then jump onto the Sand Tide so you can reach the Dragon Coin up above.
Then, if you have been to the Yellow Switch Palace, there will be a Yellow Block that contains a Super Mushroom.
Go to the right and hit the Midway Gate, then go through the pipe.
Part 2
Before you go to the right, jump onto the pipe and go left, get up against the wall, and jump straight up to hit a hidden Prize Block that contains a Cape Feather. If you try to jump on top of the hidden block, be careful not to go to the left, because you can end up losing a life if the game thinks that you were crushed in the wall. It's recommended to wait until the Cape Feather floats down to where you can see it.
Go to the right and hit the Prize Block to the right of the pipe to get Yoshi Wings. If you don't have Yoshi or you don't want to take the Yoshi Wings, skip this paragraph. If you have Yoshi and you take the Wings, you will go to an area with coins and Dragon Coins, and Yoshi will be Blue Yoshi from then on. Fly to the right collecting the coins, then fall down where the arrow of coins is pointing, and you will complete the level. Your Yoshi will stay blue, and the path to the west will unlock and you can go to Valley Ghost House. Blue Yoshi will grow wings if it has any color of shell in its mouth, and can fly until you make Yoshi spit out the shell or until he eventually swallows the shell.
If you didn't use the Yoshi Wings, you should Spin Jump off of Yoshi if you have one, because riding around on Yoshi makes you too tall to get through the next area. Go to the right and wait for the hallway in the Sand Tide to come down to where you can jump into it. As you make your way through this area, be careful not to get crushed against the platforms as the Sand Tide goes up and down.
In the bottom right, there is a dead end with two coins. When the Sand Tide is going upward, you can go through the path above that, hide in the gap at the top, then go to the right when the Sand Tide starts going back down (but if you're riding Yoshi, you'll be too tall and will lose a life). After you get past the platform below you, go down and left to get a Dragon Coin.
Go right and you will see a Dragon Coin in the upper-right of the screen. In order to get it, wait for the Sand Tide to be going down so you can hide in the gap beneath the Dragon Coin, then go to the right when the Sand Tide starts going up again, then go to the left when the Sand Tide goes near the top. Go to the right from that Dragon Coin as soon as you have gotten it so you can avoid being crushed as the Sand Tide goes down. Don't go through the lower path because it leads to a dead end. When the Sand Tide goes back up, take the upper path, then when it goes back down, hide in the pit in the middle. Go to the right when it goes back up so you're in the gap in the ceiling. Stay in the left side of that gap when the Sand Tide goes back down, and you can optionally go left to get four coins, then run back to the right to avoid getting crushed. Stay where you are again, then when you are are getting close to the lower path, start running to the right so you can reveal a hidden 1-Up by going down toward the bottom-right corner, stopping two squares before the right wall, then as soon as the Sand Tide has gone all the way down, run to the right wall to make the 1-Up appear. Then quickly run left so you don't get crushed.
When the Sand Tide is going upward, go to the right to reach the gap in the ceiling, then when it starts moving downward, run to the right to go past the two "steps" on the left, and when you reach the bottom, keep running to the right until you are just past the low ceiling. If you didn't get the hidden 1-Up Mushroom mentioned in the previous paragraph, the area above has a hidden 1-Up Mushroom instead. (If the area above has a pipe on the right, you went too far.) To get the hidden 1-Up Mushroom (which, as mentioned before, will only be there if you didn't get the other hidden 1-Up Mushroom), stand beneath the hole in the ceiling and wait for the Sand Tide to start going up, and start pushing to the right while holding the run button. Crouch for a moment on the spot one square to the right of the stationary ledge, then go to squares right and crouch for a moment there, then go all the way to the right (you won't get crushed even if you're tall because the Sand Tide doesn't go all the way up). If you did it correctly, the 1-Up will appear.
Go back to the left, then when the Sand Tide has gone all the way down, go to the right and keep running right. If you want the four coins on the right, you will have to wait for the Sand Tide to go back down. When you're ready, go through the pipe on the right.
Part 3
Run to the right so you don't get crushed by the rising Sand Tide. When the ceiling opens up, don't go down to the bottom yet. If you don't want to go to the Secret Exit, skip this paragraph. If you want to go to the Secret Exit, stand on the end of the Sand Tide that isn't covered by the ceiling, then jump up and left to reach a hidden passageway above the screen. Go to the left until you fall down into the area where there is a key and keyhole. Put the key in the keyhole to complete the level. The path to the north will be unlocked and you can go to Valley Fortress.
If you didn't go to the Secret Exit, then to the right of the pipe where you entered this area, there is a Mega Mole. Jump on it to reach the ledge on the right. Then, to the right, if you have been to the Red Switch Palace, there will be Red Blocks above the Munchers in the pit, so you won't get hurt if you fall off the Mega Mole in this pit. Jump on the Mega Mole and use it to reach the ledge on the right.
The next Sand Tide won't start rising until you jump onto it, so once you're on it, just run and jump quickly to the right so you don't get crushed. After that, there is a pit of Munchers, but if you have been to the Blue Switch Palace, the Munchers will be covered up by Blue Blocks. Jump on the Mega Mole to reach the ledge on the right, then go to the right and go through the Giant Gate to complete the level.
After the Level
If you went through the Secret Exit, the path to the north will be unlocked and you can go to Valley Fortress. If you went through the Giant Gate, or got the Yoshi's Wings and completed the Yoshi Minigame, the path to the west will unlock and you can go to Valley Ghost House.