Villains are characters with evil intentions, typically for personal gain. Some villains are open about their sinister ways, while others prefer trickery.
While Shin Mao actions are not considered criminal, his ignorance and arrogance with Mao Mao because his small size and only cares with five sisters caused permanent mental damage for Mao Mao, which affected his personality as well. Ironically, without golden armor, Shin Mao actually smaller, shorter, and weaker than Mao Mao.
The Sky Pirates are recurring villains in the show. Led by Orangusnake, the group performs various acts of theft and vandalism, with the ultimate goal of acquiring the Ruby Pure Heart to take over the world.
Rufus and Reggie are a pair of con artists. They invented a fake holiday, "Takesgiving Day", to trick the Sweetypies into giving away their valuable items. The scam lasted a few years until Mao Mao and Badgerclops moved to Pure Heart Valley, where the heroes stopped the scammers. After attempting a few more scams, they are beaten up by Adorabat and sent tumbling into the sewers.
The Thicket Thieves were a group of cybernetically-enhanced criminals who liked to mug people. The group's membership consisted of Tiny Toad, the leader, and his henchman, Bullmozer, Ratracer, and a young Badgerclops. The group's current status is unknown.