Wow, thanks a lot for your positive feedback! I am really happy you like the progression and the characters ☺️
Yes, everything was done in a single week. Originally I wanted to spend only 2 days on the game jam, because I was kind of on vacation in Spain and rather wanted to go outside. So I worked around 14 hours on this game each of the first two days. By then, around 50% of the current game were done (but without any sound or music). However I liked the game so much myself that I really wanted to keep going. But because I had already done so much in the first 2 days, there was more than enough time for me to finish the game.
Only thing I did before the jam was to look a bit into how platformers work in GB Studio for an hour to get a rough idea of what could be done, incase I wanted to build a platformer. But I did not use any of my previous test projects. I'm not even sure I saved them.