Hi, welcome to the 64 section
If you have a simple single question like this concerning a character, please ask in the character thread (in this case:
Fox thread). If you have a more general question, there is the
Ask a question thread.
As rpotts said, I think most people (including myself) slide with the thumb from left c to b, then press b a second time. Learning this technique is useful because the timing of sliding from c to b is the same whether you shine or laser. A few random tips:
-Don't do it while running (because of the lower short hop), because the whole thing becomes possible only if frame perfect.
-Don't mash b for the second laser, learn the timing instead. This is very important, because you want the second laser to be as low as possible.
-If you full jump, be quicker on the c press (you need to press it at max 3 frames to short hop).
-If no laser comes out, either you were too fast on the b press, or you pressed b too lightly (and didn't actually press it).
Concerning Melee, you'd better ask directly in the Melee section, but what I do is the same as in 64: slide from y to b.