The Portal franchise is one of the most mind-bending, physics-defying puzzle games ever. So why not up the ante by throwing in some time manipulation?
The gameplay campaign Thinking With Time Machine for Portal 2 does just that. The mod, created by Steam user Ruslan "Stridemann" Rybka, adds a time-bending record/replay-an-echo mechanic to Valve's well-known Portal formula. Similar to the gameplay mechanic found in the indie-puzzler The Misadventures of P.B. Winterbottom or one of the later stages of Braid, Thinking With Time Machine lets you be in two places at once. After recording your actions for a short time, a doppelganger appears and retraces your steps—picking up items, pressing buttons, creating Portals, and so on—leaving you free to perform other actions.
While some of the test chambers lack the "Valve polish" we expect from official Portal puzzles, most of those in Thinking With Time Machine are smartly designed with just the right level of difficulty. As you progress through the game, you have the feeling of playing co-op with yourself. You're constantly mapping out how and when each character must act--you just happen to control them both.
My biggest complaint is some of the game's early puzzles are built primarily around the record/replay mechanic, with portals taking a back seat. The first handful of test chambers were equipped with very few walls where a portal could be placed--and the few walls that did were hard to distinguish. (On several occasions, I found myself launching blasts from my Portal gun at random walls in the hope of finding the single spot I could anchor a likely-puzzle-solving wormhole.) But that gripe is small, and largely remedied in later test chambers where the Portal gun again plays a more prominent role.
Beyond that, my only issue was the length. Just when I felt the puzzles were hitting their stride, finding the right balance of portal and doppelganger gameplay, the game ended. Then again, Thinking With Time Machine is fan-made and completely free (though it does require a copy of Portal 2 to play), so it's hard to fault it for being short.
