The Monsterizer (1975)

The Monsterizer and his gang of monsters kidnap prominent citizens of Good Haven, including the Mayor and Police Chief. They are then transformed into monsters by a device, creating more lackeys for the Monsterizer. The Mighty Heroes respond to a call for help. They attempt to reason with the Mayor and Police Chief, but instead get captured. The heroes are put into the Monsterizer's machine, with Rope Man used to tie them up. The heroes can't escape without snapping Rope Man in two. But Diaper Man uses his milk bottle to prevent the Monsterizer from activating the device. That gives the heroes enough time to escape. They eventually overpower the Monsterizer and change the Mayor and Police Chief into their old selves.

Unfortunately the movie The Monsterizer is not yet available on HBO Max.