Made some improvements to the world-within-a-world effect.
The key part now is that gameplay objects (such as the door, button, and boxes) are enlarged when you shrink down. Previously, it was just the environment. This makes the transition look much smoother.
It is also based on time instead of frame rate.
Finally, the duplicate instances when the final level is grown are moved inward instead of popping in. Technically, this doesn’t make any sense, since you are shrinking down into the world, so the duplicate instances should grow outward. However, this looks fine and the effect lasts 2 seconds, so I’m going with it! 
It could of course use some more polish, and I do plan on coming back to it later. However, it’s pretty good so far!
Another thing I worked on is the dark mode collider effect:
This isn’t quite what I want, but it’s a good start for now.
I’m mostly posting it here as a reference to compare against later.