These are researches for what the end levels could look like. at the time I write this, I have actually no idea how it is now in the game. I hope I don't spoil you too much :D
There are also proposals of how the boss transition phase will look and how it spawns aswell.
Art direction by Alexandre Chaudret: https://www.artstation.com/eyardt
Developed by Lightbulb Crew and published by Focus Home Interactive.