itch.io

If you are downloading it on PC you have to go to the website, for some reason it isn't working for the itch app.
If you aren't downloading it on PC or the website isn't working then I'm sorry, I don't know what to do in that case but hopefully someone will post with a similar issue to yours found out.

I can't wait to see what new enemies are added into the next update.

The codes unlock the levels. It's useful for playing again so that you don't have to go through levels a second time or if you just want to go in real quick for the gaallery.