Successfully knocking over earthlings yields coins that are required to complete the goals set in each level. Each earthling has a different ability that can be used for causing mischief, such as boomboxes, vacuum cleaners or bazookas. Once he has beamed a person up, he can change his form by stepping under a UFO. Since Cosmi is vulnerable in his small alien form, he must first beam up a nearby earthling in order to create a disguise for himself. Of course, panic arises and reporters try to get a snapshot of the little alien, but Cosmi accidentally pushes someones camera around, causing it to take a photo of the crowd, thus revealing that several of them are also aliens. Cosmi wins and travels back to Planet Mischief to celebrate, but crashes into another TV-station and crashlands on Earth again, this time, in the middle of CocoTown square. Itazura uses their trap as the final challenge for Cosmi, and challenges him personally there. It is revealed that Cosmopolis is a trap for 'Anti-Alien-Forces' to capture all of the aliens on Earth by disguising themselves as aliens. He takes him to his Dojo to train, and lets Cosmi move on with his mission, on 8 different locations: CocoTown, HighStakesHill, Pranksyvania, PharaohIsland, BigBootyBay, FrontiersVille, RaccoonCity and finally Cosmopolis. When crash landing, he manages to hide in an alley on Coco Town, where he is saved by Earth's Mischief Master, Master Itazura. Cosmi crashes with a TV satellite from a town called Coco Town. Cosmi, a three-year-old alien, travels to Earth for his mission, in order to impress his father, the Master of Mischief, Cosmi Sr., mostly because Earth is considered the greatest challenge.
The story revolves around the Planet Mischief, where there is a tradition that once someone turns 3-years old, (s)he must travel to a planet and learn how to perform 'Mischief' and cause panic on that planet.