As we mentioned in our review, Yooka-Laylee and the Impossible Lair utilizes a mechanic that will make over some levels with a new theme, basically giving you two levels in one. Wondering how that idea came about? Playtonic's Dan Murdoch explained in a Reddit AMA.
Ok, so the 'two levels in one' thing originally started as a way to make more levels quickly using less individual pieces of scenery. This wasn't just a budget thing, it's a RAM thing. We wanted a game that played at 60 on switch as well as having good loading times. It was an experiment to see if levels that shared scenery could be loaded quicker.
However, we realized that in order to make the second version of a level interesting and different, it needed so much changing to it that it would have been quicker and cheaper to just make a separate level.
BUT!!! by that time we found that the real gain from the 'two levels in one' was not making development easier (actually it made it harder); it was that it tied so well to the overworld.
Suddenly we had a game cycle where every 2D level had a Zelda style puzzle to solve on the overworld to reveal the second state. That was such a cool idea that it became one of our main features.