Fireboy & Watergirl 4: In the Crystal Temple

Fireboy & Watergirl 4: In the Crystal Temple is a cooperative puzzle platform browser game developed by Oslo Albert, released on March 29, 2013. It is the fourth entry of the Fireboy and Watergirl series. Originally released in Flash and later remade to HTML5. Players can control both characters alone or play with a partner to guide Fireboy and Watergirl through a mysterious temple filled with crystal portals. Fireboy survives lava but dies in water. Watergirl can walk safely in water but is killed by lava. Green toxic slime is deadly for both of them. The signature new mechanic of this game is crystal portals. Portals of the same color connect to each other. Both characters and boxes can teleport through portals, and some portals need levers to activate, making puzzles more complex. It also keeps classic mechanics from previous games including icy floors and light beam puzzles. Collect red, blue and grey gems, and bring Fireboy and Watergirl to their respective exits to complete stages. It features simple cartoon graphics and keyboard controls, and is one of the most famous 2-player cooperative browser puzzle games.

These games get the keyboard directly — the controls are whatever the game itself defines, usually in its own help or options screen. Some games show on-screen buttons on phones.