Of all of the games that were involved in the
Portal 2 ARG promotion, the one that most resembled Valve's puzzle shooter series is
The Ball from developer Teotl Studios. This weekend
The Ball dev team posted up its own behind-the-scenes account on making the original
Portal 2 content that was put into its own puzzle-shooter.
After putting in a couple of obscure content items in the game, the big new addition is a new challenge level where players navigate the Ball through a series of
Portal-related test chambers. The level took about a month to complete. The article also gives clues to some hidden items in the game's terminal screens.