Set The Unnamable aside. It keeps all tokens and attachments.

Remove each location from the game (or place it in the victory display if it has Victory X and no clues on it). Investigators are not defeated during this process. (Other enemies and attachments at those locations are discarded.)

Shuffle the set-aside Mysterious Stairs locations and put 5 of them into play in a vertical line. Remove the remaining Mysterious Stairs location from the game.

Place each investigator and the set-aside The Unnamable enemy at the topmost Mysterious Stairs location, revealing it.

Search the encounter deck and discard pile for both copies of Locked Door and both copies of Secrets in the Attic, and remove them from the game.

Shuffle each set-aside copy of Endless Descent into the encounter deck, along with the encounter discard pile.