@kanity first of all, thank you so much for being patient while we got up a version that you could play and then ALSO leaving such a great and detailed review!
I am the one responsible for the difficulty of the 5th level (the cop level) and dont worry, it haunts my nightmares as well.
I designed a good portion of the levels before we had some of the mechanics implimented (like the goo and the cops). So by the time the stuff was working as we intended, it was fairly close to the deadline. Naturally that was when I realized some of the levels were really difficult. I found it was much easier to try and tweak the rest of the level instead of the cops since they were animated, but that created some unintended jank. The vision cones sometimes interact inconsistently with some of the rest of the level assets which creates some very frustrating areas.
I went back and tried to make level 5 a bit more manageable and thought I did, but there is that one area you mentioned near the bottom that is hellish. For whatever reason the vision cone there is so unforgiving and I really wish I had noticed that in one of my playtests, because when we finally released and I got to that level I also struggled for like 30 attempts before I finally figured out I have to wedge myself in the corner to get past him.
That and the goo are definitely things I would adjust/change if I could go back, but oh well.
As for the player going through the boxes, yeah thats kind of an annoying visual bug and issue that has to do with the characters collision only covering about half his body (this is so that your head isn't consistently bonking into things while walking. It mostly has to do with what layers things are on and sometimes I couldn't figure out a good way to avoid it. For example, in your last image in your comment #1, the fences are all on layer 3 while the player is on layer 1. This is so that the player can walk behind the fence and you get the illusion of him being actually behind the fence. However, when he gets down below, because his head has no collision, he ignores the collison on the bottom of the fence and so the illusion is broken as his head passes through.
ANYWAY There is definitely a lot I wish we had time to go back and fix, but overall I think that if you can beat level 5, you are a true gamer and have a great amount of determination, so I applaud you!
Thanks so much for playing and glad you enjoyed it!