Boxhead 2Play

Boxhead 2Play is a top-down zombie survival Flash shooter developed by Sean Cooper and released in 2007, a landmark entry of the Boxhead series and the first in franchise to feature local two-player gameplay. It has three game modes: single player, 2-player co-op survival and 2-player deathmatch. Four box-headed characters and 18 unique arena maps are available with adjustable difficulty settings. Players start with a pistol. Build kill combos to unlock shotguns, UZI, rocket launchers, flamethrowers, grenades and more weapons. Enemies include regular zombies, fast undead and ranged devils, growing stronger with each wave. You can build barricades to block zombie encirclement. Player 1 uses arrow keys while Player 2 uses WASD with separate fire controls. Featuring simple block graphics and intense multiplayer action, you can team up with friends against zombie hordes or fight each other in PvP. It is a famous 2-player zombie Flash game widely popular on Chinese browser game portals.

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.