Extra-Terrestrial is a single screen side view shooter where it is your mission to destroy an alien invasion that is threatening Earth. You control a missile launcher that starts on the bottom of the screen which you are able to move around the screen as UFO's appear from above. To fire a missile you first must load before you can fire by pushing forwards. If you hit an UFO then fallout from the explosion falls to Earth and this must be avoided and if you hit the fallout or an UFO then you lose one of three lives. Before you play, you can select a level (1-3).