Gameplay Single-player thumb|250px|left|Screenshot of the player engaging a robot from a cockpit perspective. The yellow number and adjacent bars in the HUD represent the amount of total energy. Also in the HUD, counterclockwise from top left: the available extra lives, an enemy missile lock indicator, a colored key inventory, the selected primary weapon, the player ship's shields, the selected secondary weapon, and the score count.
Gameplay Single-player thumb|250px|left|Screenshot of the player engaging a robot from a cockpit perspective. The yellow number and adjacent bars in the HUD represent the amount of total energy Also in the HUD, co.unterclockwise from top left: the available extra lives, an enemy missile lock indicator, a colored key inventory, the selected primary weapon, the player ship's shields, the selected secondary weapon, and the score count.