Exerion is a vertical shoot 'em up released by Jaleco in 1983 and licensed to Taito for distribution on the United States. Exerion is a shoot 'em up game featuring parallax effects and inertia simulation, something notable for 1983. The player travels around strange scenarios shooting aliens. The player has two types of guns: fast single shot (limited) or slow double shot (unlimited). In 1987 the game was followed by the semi-sequel called Exerizer. Source: Wikipedia, "Exerion", available under the CC-BY-SA License.