Hey, fun platformer, quite challenging (at least in 509 and a couple more.) For those having problem with 509 (SPOILER):
For some reason the game forbids you to wall jump off the left side of the first ledge, if you have reached it wall jumping from the eastern most wall. To reach the left side, and still be able to jump off it, you must have jumped from the right side of the ledge, not from the eastern most wall.
That's a bit tricky, actually. I'll try to explain it step by step.
1- Wall jump off the ledge and the easternmost wall. You should try to get, with the last wall jump, on the right side of the ledge, just below the red point on the tip.
2- While jumping this last jump, KEEP THE LEFT KEY PRESSED.
3- As soon as you reach the right side of the ledge, just below the red point on the tip, press the right key once, BUT KEEP THE LEFT KEY PRESSED.
4- You should somersault over the ledge. Now, press the right key as you fly over it. Try to reach the left side of the ledge, without touching the red tip. It's quite difficult, and I admit I did it by luck.
5- Wall jump off the left side of the ledge. It should work.
6- Use your air jump (you still have it, if you followed my instructions and didn't make any mistakes) to reach the westernmost ledge.
7- Jump off the western most ledge, and to the middle ledge.
8- Jump off the middle ledge, and reach for the sky!