Portal 2 adds features including tractor beams, lasers, light bridges, and paint-like gels that alter player movement or allow portals to be placed on any surface. In the new cooperative mode, players solve puzzles together as robots Atlas and P-Body (both voiced by Dee Bradley Baker).In the single-player campaign, players control Chell, who navigates the dilapidated Aperture Science Enrichment Center during its reconstruction by the supercomputer GLa DOS (Ellen Mc Lain); new characters include robot Wheatley (Stephen Merchant) and Aperture founder Cave Johnson (J. Jonathan Coulton and the National produced songs for the game.
The initial tutorial levels guide the player through the general movement controls and illustrate how to interact with the environment.
The player must solve puzzles using the 'portal gun' or 'Aperture Science Handheld Portal Device', which can create two portals connecting two distant surfaces depicted as matte white, continuous, and flat.
Before Portal, Aperture Science conducted experiments to determine whether human subjects could safely navigate dangerous "test chambers", until the artificial intelligence GLa DOS, governing the laboratory, killed its employees.
At the end of the first game the protagonist Chell destroys GLa DOS and momentarily escapes the facility, but is dragged back inside by an unseen figure later identified by writer Erik Wolpaw as the "Party Escort Bot".
Paint-like gels (which are dispensed from pipes and can be transported through portals) impart certain properties to surfaces or objects coated with them.
Only one type of gel can affect a certain surface at a time.
When Chell dies in the single-player game, the game restarts from a recent checkpoint; The goal of both campaigns is to explore the Aperture Science Laboratory—a complicated, malleable mechanized maze.
While most of the game takes place in modular test chambers with clearly defined entrances and exits, other parts occur in behind-the-scenes areas where the objective is less clear.
Some surfaces, such as grilles, cannot be coated with a gel.