Here's a list of all issues and personal suggestions I could think of while playing the level, in case you're interested in releasing an updated/expanded version:
- I spotted SGEs here and there in some areas. Some of the blocks in the left wall on the bottom part of the frozen castle have black borders while others don't, which looks a bit weird. I also recall seeing some borderless tiles while running around in the dark maze area, and a few corners missing on diagonal tiles (e.g. the roof on the house in the starting screen). This last one is just a trivial issue for me, though, as I don't think it looks bad as it currently is.
- You can trigger a void screen at x1015y1015, if you walk to the left after opening the main door of the frozen castle.
- Another void screen can be reached by climbing the left wall in the screen with the frozen princess (x1011y1016, and possibly its duplicates). Also, it's a bit tricky to climb up to the upper area on that screen (which is why I tried climbing the left wall and jumping from it). Some 2-way platforms or floating blocks would help.
- It doesn't really matter, since the game is autosaved after freeing the frozen princess, but killing the player with invisible tiles is not a very elegant way to block the path back to the screens below. Simply putting any solid tile (preferably something that looks like a closed trapdoor) would be more appropriate.
- The visible radius of the black overlay in the dark maze area is very small. This is not a problem while you're just running thorugh the small corridors, but it can be quite annoying when enemies and deadly obstacles are present, as this causes many unfair deaths. The screen with the sliding spike traps is an especially bad case, since those tend to move fast and erratically and it's very hard (practically impossible, at least for me) to react in time when one of them enters my very small field of view. I'd suggest making the radius of the black mask at least double the current size in these screens.
- The screen where you have to jump between floating blocks with eaters may be a bit too tricky for a "Normal" difficulty level. It's not hard once you figure out the intended solution, but it might be a problem if the player ends up thinking they're missing a power-up.
- For cutscenes, consider using "Sticky" and "No Jump" objects (or Bank0/Obj49, since you're using KS+) to prevent the player character from moving at all, instead of just blocking the path. This way, you won't hear footsteps during the sequences, even if the player tries to run/jump.
- The sudden changes in music while transitioning between some screens felt a bit weird. I think it's a better idea to stick to a single song for an entire area, for a more cohesive experience. Also, the lack of ambience sound in most areas was somewhat disappointing :/ Consider adding some wind, running water and other cave background noises to the different areas, as this can add a lot to the experience.