Hey Skyboy! I picked this game up, and I am actually working on an achievement set for https://retroachievements.org/
I have a few questions that I have discovered playing and working through the game.
1) I observed that your score counter does not appear to properly count the score once you pass 65,535 it starts to loop in a weird way.
I noticed that memory address 0x0355 appears to be the roll over, but that roll over does not appear in the game score properly.
2) How many Danger Levels are there? I have only managed to get to level 2 before I started playing with the memory, and I am getting interesting results (second image setting the 0x0304 to FF) XD
I think I have found everything I need at the moment to work out some good achievements, and just wanted to head to the source to see what your thoughts were on the matter.
I did not notice any additional difficulty (beyond the timer reducing with each danger level) so I was likely going to chop the achievements at danger level 2 cause beyond that it seems like there is no real way to survive it once the timer drops faster than you can heal each stage.
This has been a very fun game man, Would love to see more, but giving me a reason to dust off my zapper and having it actually run better than duck hunt was super impressive to me.