Wacko is a 1983 arcade game by Bally Midway. It debuted during the "Golden Age of Arcade Games". It featured a unique angled, or "sloped" cabinet design and a combination of trackball and joystick controls.
The player assumes the role of Kapt'n Krooz'r, a small, green alien within a bubble-topped spaceship. The goal of each level is to eliminate the monsters, accomplished by shooting twin pairs in succession. As the player progresses, shooting monsters out of order creates mutants that must be unmatched before they can be eliminated.
The player moves Kapt'n Krooz'r with the trackball and fires using either joystick. (A similar shooting scheme was used in Robotron 2084, although in 8 directions rather than 4.) Shooting a single monster stuns it for a few seconds. Krooz'r must then shoot the monster's twin before the first one recovers in order to eliminate the pair.
Shooting a different monster, on later boards, results in the two becoming a mutant—the head on one joins with the torso on the other, and vice versa. To eliminate these mutants one must either "unmix" them, by shooting the same pair again, or produce a second set of identical mutants which can then be paired up with the respective members of the first pair. Eliminating a pair of mutants is worth more points than eliminating a pair of non-mutants.