The Plastic Blaster (1975)

The Raven, a villain whose hideout is hidden in a mountain near Good Haven, attacks the city with his "plastic blaster" gun. It seals its victims in plastic. The Mighty Heroes respond. Eventually, the Raven (aided by his flock of villainous birds) gets the upper hand, sealing Tornado Man, Rope Man, Strong Man and Cuckoo Man in plastic. Diaper Man sneaks into the Raven's hideout and in the fight that follows, the other heroes are free. After disposing of the Raven's flock of birds, the villain is about to strike again. However, Diaper Man flings his bottle, jamming the barrel of the plastic blaster. It is now the Raven who's sealed up.

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