There are two different characters in the game, who are Keen and Mortimer, as they battle each other. They can be controlled by either a person or the computer, which can be set throughout accessing different executable files. They play similarly, although Mortimer's shots can take out Keen in one hit while Keen's shots can take out Mortimer in three hits. Mortimer's shots can also be able to destroy non-border blocks by hitting the blocks a few times. Keen can be able to duck under Mortimer's shots.