Portal 2 alpha and beta development stages. Unused intros, ending, mechanics and puzzles. Wikipedia: Initially, Valve planned to exclude portals from Portal 2. For five months, they focused on a gameplay mechanic called "F-Stop"; Valve did not discuss the specifics of the idea as they may use it in a future game. Though the playtesters liked F-Stop, they expressed disappointment at the omission of portals. Following a report in Kotaku about some leaked plot elements, Newell directed the team to reconsider. https://twitter.com/NeoGamerbr Source: GDC Panel Portal 2: Creating a Sequel: https://www.youtube.com/watch?v=BYFvwbby2YM