You know, magic ¯_(ツ)_/¯

Yes, it is irrelevant in this example. I'm guessing the kata is judged just by the structure of the function.

The one wich is at the top of the stack

If it does, or if you want to make a new one, feel free to copy your code over. You just have to make sure it is ready before you publish. In this case I'd suggest mostly just a much better description, and maybe one or two instructions that make use of the registers (maybe ADD - Add values from registers x, y and add to output or something).

If you are unsure, keep in mind that you can still share the link to the kata before it is published, and people can try it (they just can't submit solutions). If you look in the sidebar you should be able to find the Gitter channel specifically for helping people write katas. If you go there, im sure someone can test it out and let you know problems, even before you publish.

I would suggest taking it down until you fix it. You are one bad review away from it being retired anyway.

Which may not be a bad thing, you can take this as a learning experience and build a new and improved one, see how it goes.

The second half of my previous comment says how to know what the test case is.

When you find a test your code fails on you should be debugging that particular test case, not other ones.
If you weren't already aware, you're free to print out anything you like to see, for example the input.