Portal 2

In Portal 2 the player returns as Chell, having been in stasis for several hundred years while GLaDOS and the rest of the Aperture Science facility has fallen into disrepair. Chell is awakened by one of GLaDOS's personality cores, and inadvertently wakes GLaDOS; GLaDOS is immediately displeased at Chell's return and begins testing her again through numerous chambers as she rebuilds the dilapidated facility. Portal 2 continues to challenge the player through numerous platforming and physics-based puzzles using the Aperture Science Handheld Portal Device (ASHPD, also dubbed the "portal gun"), a device that can create a temporary hole between any two flat surfaces. Other gameplay elements are added to Portal 2 including tractor beams, laser redirection, and special paint-like gels, taken from the Independent Games Festival-winning DigiPen student project Tag: The Power of Paint, that imparts special properties to objects it touches such as increased momentum. Portal 2 also includes a two-player co-operative mode, each player-character a robot that has become self-aware from GLaDOS' influence, and requires the players to work together with their own portal guns to complete each level.

Portal 2 will continue to challenge the player by solving puzzles in test chambers within the Aperture Science Enrichment Center using the portal gun (the Aperture Science Hand-held Portal Device), a device that can create two portals connecting two surfaces across space. Players, as the silent protagonist Chell from Portal, solve puzzles by using these portals to move unconventionally between rooms or to use the ability to fling objects or themselves across a distance. The functionality of the gun has not changed between the games, but within Portal 2, players can take advantage of the bleeding of other physical effects through the portals.Game Informer identified two examples of this: one was the ability to use air currents created by Pneumatic Diversity Vents, a series of transport pneumatic tubes, through a set of portal openings to push a turret over or to draw objects into the suction.The second example was to use the power of Excursion Funnel tractor beams through portals to bring Chell or other objects to otherwise inaccessible areas.The game also introduces special paint-like gels that can be used to impart certain physical effects to a surface such as Propulsion Gel that boosts Chell's speed as she crosses a surface, and Repulsion Gel that allows her to jump from a surface.The player will be required to determine how to transport that gel to appropriate surfaces using portals in order to progress.The gels can also be applied to objects, such as the Weighted Storage Cube crates, that affect their own physical nature.In addition to the Storage Cube, there are new types of portable objects that assist the player, including Redirection Cubes with mirrored, reflective surfaces used to redirect Thermal Discouragement laser beams, Aerial Faith Plates that can launch objects placed on them, and spherical Weighted Storage Balls, which made a brief appearance in the original game in one of the advanced chambers.A further new concept includes Hard Light Bridges that can be crossed when lit, and can be extended and redirected through portals.

While most of the single-player game will take place in the test chambers created by GLaDOS or her personality cores, there will be times where the player will need to move behind-the-scenes in areas beyond the test chambers as they are reconfigured, leaving the player free of GLaDOS's observation and control.

The game will include a two-player co-operative mode in addition to the single player mode.Both players control separate portal guns and can use the other player's portals as necessary; each player's portals will be of a different color scheme (blue/purple, and orange/red) to help distinguish between the two sets.Because of the number of possible portal combinations, the test chambers that the players proceed through are much more difficult than the single-player campaign, encouraging the two players to work together. This includes complicated laser redirection using both series of portals, or working in two separate chambers, performing actions in their side of the chamber to allow the other player to progress in theirs. Should either robot die, a new robot will be recreated shortly after, allowing players to continue on the puzzle.The game includes voice communication between players for this mode as well as split-screen for players playing locally. Online players will have the ability to temporarily enter a split-screen view to help coordinate actions.Players have the ability to place icons on the game's levels as a means of informing the other player what they need to do, and perform emotes with their partner, such as waving or hugging. Valve has stated that both the single player and the co-operative campaigns are about each twice as long as the original campaign in Portal. Erik Woplaw estimates each campaign is about six hours long.

As with previous Valve games Portal 2 will contain in game commentary from the game developers, writers, and artists. The commentary, accessed after completing the game once, appears on node icons scattered through the game's levels where the development team found significant changes from their original ideas, or where ideas failed to work out for the game.