Hey, I like your game and the style. I'm playing it on my Gameboy Color with a flashcard. Even on easy mode it is pretty hard for me (my thumbs are burning haha). I haven't finished it yet, but I found some bugs (or features?).
1) Right after the first mini boss in level 3, the 2nd screen: when I jump on the ice platform and back, the platform disappears, then I can jump from the upper left corner staight on the ladder bottom right: it teleports me without any damage back to the upper left corner.
2) Close to the end of the 2nd phase of the main boss in level 3, after defeating the little enemy, I stood far left and the boss flew from far right over me off the screen and never returned.
3) First screen of the beach/water level: sometimes the jumping doesn't work properly (jumps only few pixel high) resulting in unmanagable swimming (here I got stuck)
I appreciate your effort and your work! Keep it up :)