I wanted to mention that I have 100% absolutely everything in the US Super Princess Peach.
I have caught Stafy, who I believe is just called Starfish, by killing him in all three spots he appears. I did not have any sort of Stafy game in my GBA slot at the time (or ever).
The Koopa Kid thing is really neat! I expect it will definitely show up on TMK at some point, perhaps with your work cited.