Portal 2 Gameplay

A representation of how the magnitude of linear momentum is conserved through portals. By jumping into the blue portal, the character is launched out of the orange portal and onto the platform on the right.

A more advanced portal technique. The character builds up speed using two blue portals, to reach an otherwise unreachable area. The second blue portal is carefully created mid-air, after exiting the orange portal for the first time, destroying the first blue portal in the process.

Portal 2 is a puzzle game presented from the first-person perspective. Normally, the player, as either Chell in the single-player campaign or as one of two robots, Atlas or P-body, in the co-operative campaign, can move, look, and carry and drop objects, as well as interacting with switches. The goal is to maneuver the characters through a number of test chambers in the Aperture Science facility, traversing the chamber from the start to the exit. Though the player-character can take some damage for a brief period of time, they will die under sustained injury and be restarted at a recent checkpoint; however, characters are equipped with "long fall boots" that absorb the shock of landing after a large vertical drop. The player must figure out how to overcome seemingly-bottomless gaps, evade pools of toxic liquid, or avoid line-of-sight or even disable robotic turrets to safely arrive at the exit.

Initial levels provide a tutorial on general movement controls and interactions with the environment. After these levels, the player will be required to solve puzzles in test chambers within the Aperture Science Enrichment Center using the "portal gun" (the Aperture Science Handheld Portal Device), a device that can create two portals connecting two surfaces across space. Players 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 transmission of other physical effects through the portals. One example is the direction of Excursion Funnel tractor beams or Hard Light Bridges through portals to provide surfaces or areas which the player can use to move the player-character or specific objects across obstacles. While early technology demonstrations included the use of Pneumatic Diversity Vents, a series of transport pneumatic tubes, and the interaction of their suction or venting power through portals, these do not appear in the final game, as the technology was not quite perfected by release.

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 bounce from a surface. A third gel type, Conversion Gel, allows any surface coated with it to accept portals. 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 Aperture Science crates, that affect their own physical nature. Water can be redirected to wash away gels applied by the player, returning the surface or object to its normal state. In addition to the returning but cosmetically redesigned Storage Cube, there are new types of objects that assist the player, including Redirection Cubes with prismatic lenses used to redirect Thermal Discouragement laser beams, Aerial Faith Plates that can launch objects placed on them, and spherical Edgeless Safety Cube, which made a brief appearance in the original game in one of the advanced chambers. The heart-decorated Weighted Companion Cube, used by GLaDOS in the first game to make Chell form an emotional bond to the inanimate object before incinerating it, also appears briefly in the sequel.

While most of the single-player game takes place in the test chambers created by GLaDOS or her personality cores, there are 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 includes a two-player co-operative mode in addition to the single player mode. This mode can be played by two players at the same computer/console via split-screen, or through two remote players at their own computer/consoles; Microsoft Windows, MacOS X, and PlayStation 3 users can play with each other regardless of platform. Both players control separate portal guns and can use the other player's portals as necessary; each player's portals are 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, requiring the two players to work together. Initial chambers set each robot in their own separate section of the chamber, and their solutions teach the use of the communication tools and portal use to complete.

Later chambers are less structured, and require the players to use both sets of portals for laser or funnel redirection, launches, or other maneuvers to reach the exit. Should either robot die, a new robot will be recreated shortly after, allowing players to continue on the puzzle without restarting. The game includes voice communication between players for this mode as well as split-screen for players playing locally. Online players have the ability to temporarily enter a split-screen view to help coordinate actions. Players have the ability to "ping" walls or objects on the game's levels as a means of informing the other player what they need to do, starting countdown timers for concerted actions, and perform "gestures" with their partner, such as waving or hugging. Borrowing on the concept from Left 4 Dead, players, both in the co-op and single player campaign, can see the outlines of placed portals through walls and other obstacles to identify their locations. The game tracks what chamber each player has completed, and allow a player to replay chambers they have completed with other partners who may have not yet completed that chamber.

Valve has stated that both the single player and the co-operative campaigns are about each 2 to 2.5 times as long as the original campaign in Portal, with the overall game five times longer than the original. Erik Wolpaw estimates each campaign is about six hours long.

As with previous Valve games, Portal 2 contains 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, either where the development team found significant changes from their original ideas, or where ideas failed to work out for the game.