In Last Laugh, they worked together in the guise of being freak show performers in Zombozo's circus. As his minions, they would perform to lure in an audience for Zombozo. While Zombozo would feed on the crowd, they would go out and strip the town of all its valuables. After Zombozo was beaten by Ben, they set out on their own.
In Ghostfreaked Out, they reappeared trying to steal some trophies, but were ruthlessly thwarted by Zs'Skayr. While they were hiding, Zs'Skayr found them and forcibly became their leader. A little after Zs'Sakyr was fried, the Circus Freak Trio were taken to jail.
In Ben 10,000, a future version of the group, called the "Neuvo Circus Freaks" (nuevo is the Spanish word for 'new') are mentioned in passing by Ultimos.
Acid Breath is one of Zombozo's three minions, and without a higher rank to command them, he acts as the trio's leader (with somewhat inconclusive results). His appearance is quite like that of a zombie. He has the ability to project corrosive acid from his mouth in the form of either a vapor or a liquid, a trick he implies was taught to him by his mother. This acid can easily dissolve whatever he wants it to, even metal and stone. Despite the potency of his breath, he is one of Ben's least dangerous foes. If his mouth is jammed by an object (such as a baseball), or if something causes him to cough and gag (such as when Gwen blasted a fire extinguisher's contents into his mouth), Acid Breath will be briefly unable to use his powers and will be vulnerable to attack. Even though, Acid Breath spits out acid, his own acid and gas might be dangerous to himself.
Frightwig has pale skin, a tight-fitting body suit, and five orange tentacles for hair. The tentacles are extremely powerful, giving her strength equal to that of Thumbskull. They are also tipped with metal orbs for greater concussive damage. She's also extremely nimble and skilled in acrobatics. However, she, like Acid Breath, is always easily subdued by Ben, usually by getting tied up by her own hair. During the Ben 10 Week marathon on April 13, 2008, it is said a middle-aged Frightwig leads a new trio of Circus Freaks 20 years later.
Thumbskull, as the name suggests, has a head shaped like a thumb (complete with a fingernail-like hairstyle on his forehead). He also has incredible strength (though inferior to that of Fourarms), but limited intelligence. Like his co-workers, Thumbskull is always beaten very quickly by Ben, even worse than the other two. His name is a play on the insult "numbskull," as well as the obvious appearance gag.