I didn't have much time to work on the game today, but I did finish that challenge room I was talking yesterday! It's a bit less involved than it originally was, but the challenge is much more possible and not frustrating at all if/when you fail. I've added a new enemy and that made me think that I might need more than three sprites per enemy, so I've refactored a bit of how sprites work.
Maybe I should've made only one sprite per thing total and change its color in-engine (using the SpriteRenderer Color property, for instance) but no, I've made all of my sprites in paint.net, changed all of them to red for the fire world, blue for ice, etc. So when I instantiate an enemy, by default it uses the 'base' sprite, so I have to go through some code so it changes to the right sprites depending on the world. I've tweaked that code to allow for any number of sprites, not only 3.
Time spent on the project so far: 544 hours
Currently working on: Continuing the story