This trio of thieves appears in the episode "Last Laugh" and again in "Ghostfreaked Out". 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 "Ben 10 vs. The Negative Ten (1)", they are now working for The Forever King. The Circus Freak Trio has only made three appearances in the Ben 10 Series.

Acid Breath

Acid Breath is one of Zombozo's three minions. 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 (hence the name "Acid Breath") 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.
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 blew a fire extinguisher's contents into his mouth), Acid Breath will be briefly unable to use his powers and will be vulnerable to attack.

Frightwig

Frightwig is one of Zombozo's three minions. She 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.

Thumbskull

Thumbskull, as the name suggests, has a head shaped like a thumb. He also has incredible strength (though inferior to that of Fourarms), but limited intelligence. He is one of Zombozo's three minions. 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.