This stage is fairly simple but very long. You have to be quick here or you'll be short on time. Walk to the right, avoiding the Cylinders, until you find an elevator. Take it up. Ignore the door beside you for now and carefully walk to the left, destroying the balls there. Destroy the flashing brick at the far end and then head through the door back to the right. When you reappear, walk to the left, and try to jump over the platform to left of the second door. You won't make it but the platform will disappear and you'll land on a elevator below. Take the elevator up and enter the door. Climb the ascending platforms until you reach the top.
A Cylinder will usually be floating here but it has quite a distance to travel so you have a good amount of time to jump. Wait until the two Cylinders to the right are going up and then jump to the platform ahead. Continue jumping until you reach the elevator. The last Cylinder in your way is slightly out of sync with the others so you have to wait for a second before jumping or you'll jump right into it. Go up the elevator and then back to left. Destroy the flashing brick on top of the elevator to the left, and use the elevator you're on now to go up. Enter the door at the top. When you reappear, jump to the left and head through the door at the bottom.
Shoot the flashing brick and then head back through the door. Don't bother going back up. Just drop off the side and jump back toward the two elevators. Take the second elevator up. Jump off the left side when you reach the top, and continue to the left. The leftmost platform will disappear as well as the stack below it, until you land on the elevator below. Take it up. When it stops, don't do anywhere, press up again until it reaches the top. Continue to the left and destroy the flashing brick and then head back to the right until you see an elevator below. The platform above the platform will disappear. Walk onto it when the Cylinder below isn't around and take the elevator up.
Go right and fall off the edge. Stay on the lowest platform here to avoid the Cylinder but hit the flashing brick and use the elevator afterwards to continue up. Duck under the two Cylinders ahead and enter the door. There are two different paths you can take here, but stick with the shortest one. When you reappear, face right and hit the flashing brick. A molecule will usually appear but you don't have to worry about it. After that continue up the ascending platforms to the left. When you reach the top platform, stay on the right edge of it and jump. You should land on the platform below, not the higher one, which will disappear when you fall on it.
Jump to the left twice until you reach the platform closest to the elevator. Don't bother trying to fall onto the platform to the right and jumping across like you did before; it will disappear and you'll be stuck. Instead, stand on the right edge of this platform and jump to the left. Another molecule will usually appear to the left so you have to be fairly quick. You should land on the elevator below. Take it up and enter the third door to finish the stage. Congrats, you completed the game! There's no ending, but it will say congratulations and show your score.