Inside an amusement park, a mysterious cabal plots doom. They hire Villo, "The World's Vilest Villain" to kill the Challengers. An anonymous tip lure the heroes to Excito-Land. They're grabbed by op-art paintings, swallowed by a dinosaur, tear-gassed. Three end up captives in cells. Villo boasts he holds the key. Rocky breaks in and grabs it. But as he unlocks the door, Ace becomes a giant monster! Villo splits via "vanishing beam" to his headquarters, Villo's Villa. His partner is the giant computer Brainex, and the two argue constantly. The monster wasn't in the plan (chemicals in the walls changed the explosion), but they can use him. Monster-Ace invades Challenger Mountain just as Red, Ace, and Prof zoom out in their new jet, the Gallopin' Gizmo. Monster-Ace runs wild and Challenger Mountain explodes! Villo summons the monster and the Challs follow. Rocky and Red are captured in trophy cases. Prof goes missing and Brainex stutters. Suddenly Ace morphs back to normal. Prof was inside Brainex rewiring him! Villo zaps the Challs outside with his vanishing beam, restores Brainex, and Villo's Villa soars away. And the Challengers need a new headquarters!

2