Squirrle and Racoon!? Sing me in!
Great visual changes. I loved the small details, like when you grab the underwater sunburst, the mouth of the character was as if they were holding their breath haha.
I had the same issue this time with the boss, were it would not spawn the first time I got to the lava pool. I entered the power plant, died inside, and when I reached the lava pool again, then the boss spawned.
I noticed there are a couple of small "corridor" areas like on the picture below. Unless you plan to add stuff to these areas in the future, like small collectables, I don't think you need them.They entice you to explore, only to reach a dead-end.
Inside the power plant, it is very fun to try to do the challenges "in one go", preserving momentum, but by doing that it is very easy to die, then re-spawn all the way at the beginning of the level. So I think you should add a checkpoint inside the power plant, at the door.
On the conveyor belts, my initial reaction was to jump at the very end, for the momentum to fly me over. But I noticed that kills your vertical momentum. You need to just let the conveyor belt "do the jump for you". I feel like both options should be valid.
Lastly, inside this 2D section, when doing these "loops(?)" my reaction was to first hold [Right], then [Left], as I'm upside down, but that made the character freakout, and I got stuck inside the collisions, with no way of escaping. Perhaps as you are still prototyping and ironing things out, add a button in the options to "reset" or "unstuck".
But overall I had a lot of fun. Keep it up!!