Wilderness
The wilderness is the one with the most leftovers in the files for levels. Most of it are from very early stages of development, back when it was called "Wasteland" and took place during the day. Some others are leftovers from the Gamescom 2019 demo.
There aren't as many left in the puzzle piece systems though.
The "Wasteland" version of the wilderness had it take place during the day (despite the image being dark as hell) and the front of his cabin had some stuffed mooses left there.
The kitchen was very similar to what we got, except for the stuffing coming out of the furnace and some assets' positions.
The hallway was not THAT different, but the entrance (where we find the first hat in the final game) was very different.
There is a picture in-game that is the first image of the hallway.
The basement had an entire pretty entrance downstairs compared to the one that has the staircase right in front of the door. Even had stuffed head trophies hung on the walls.
The basement was way larger in this version and it would be where Mono and Six would end up after being kidnapped by the hunter, as i discussed in the unused animations section.
The hunter's cabin was way larger as a whole. The levels are very dark, but the family's room was way bigger, the room before the attic had way more furniture and even bookshelves. The only room that was smaller in this version is the attic, which was smaller and had the old model of the stuffed granny right in the middle of it watching TV.
The shed was also WAY bigger in this version. I always assumed the hunter would walk around instead of just looping the skinning animation he does in-game. There is a picture in-game that is taken from the first room in the first picture. There's also another one taken in the corner of the second image.
Lastly, there's this version of the basement. Judging by how it looks nothing like any of the other ones, i imagine this was the very first version of it.
For the puzzle piece systems, there isn't much, but there are some very interesting ones. There are some mentioning the kids other than Mono and Six, some mentioning the Thin Man, and some cut Hunter scenes.
One i did find interesting is this TelevisionWastes. It's probably an older version of the tv scene used in the announcement trailer.
Some other interesting ones are that we would find the "Native American" hat in the wilderness, and that there would be a Scout Camp level, where we would originally get the scout hat from.
Something also interesting is that originally there would be a Glitching Remain in the attic.
EXTRA: Gamescom 2019 Demo Levels. The Announcement Trailer version of Little Nightmares 2 was sort of an in-between. It has some levels that look both close to the old version yet closer to the new version. The attic of it is still leftover in the files.