Goodbye Deponia

Very soon after Doppelganger, Rufus et al will enter a Scooby-Doo-like door puzzle, where going in one door causes someone else to come out of another one. The goal of the puzzle is to get Cletus and Donna to appear in the hallway at the same time. To accomplish this, you must enter the Seer's room twice and then go down the back right stairway.

This is one of the few puzzles in the game that can actually be reset if you mess it up. Consider the puzzle reset once Donna corners Rufus in the closet and beats him up.