Yeah, learning to let go of things you've already sunk time into making. Good thing that you managed to scrap some features that didn't work though. The key system could have been used on the challenge roomsto get a still use out of making the system. The key could replace on of the trickier nearby runes so you'd still get some use out of the system and wouldn't need too much forced backtracking. Oh and forgot to mention that one of my tries on the boss level, I actually found and got a key there which was a bit confusing and probably made it harder for me to figure out what to do. The real solution was easier than the key being there implied.
I'm not all that familiar with tile systems (especially on Godot which I pretty much just got into) but I'm pretty sure you can do composite colliders so that it'll bake them in to a single polygon instead. And of course you could always just do it manually too. Have the spike tiles be purely visual only and then add invisible killbox areas on top of them. More work of course to do it this way.
Yeah the escape sequence would have needed something more than just to go backwards the exact same thing. Quite a lot of the levels were not designed to be bi-directional. And they would even need to be harder on the way back, I think it would be pretty much the opposite and it would be just a smooth run back. Same kinda goes for repeating the same thing in a mini form on the challenge rooms. The rooms could maybe start caving in, thus adding more dangerous obstacles to make the run back trickier.
Oh yeah and the challenge room rewards started gotting stale after a few of them as it was always the same time reduction which getting diminishing returns too. It was just the completionist part of my brain compelling me to go finish them even if there was no much use. And on that same vein, it would have been nice to see the rune counts a bit better on UI. Often you couldn't really focus on the pickup number as it was in the middle of some tough platforming so it could have used a permanent place on UI. It should have also shown the total amount up to the end of that level (including the challenge rooms) so that you'd know that you're still missing some before exiting. Still annoyed about those missing five.