Following the events of Revenge of the Creature, bunch of people lead by mentally unstable Dr. Barton set out to capture Gill Man in the Florida Everglades. However, Gill Man is badly burnt during its capture and it is given reconstructive surgery that enables it breathe on land. It is then taken to Dr. Barton's place where it escapes and causes havoc.
The film would later be added to the repertoire of Mystery Science Theater 3000 alumni Trace Beaulieu and Frank Conniff in their "The Mads are Back" live movie-riffing shows.
Has the examples of:
- Asshole Victim: Grant and Barton.
- Attempted Rape: When on their way to civilization, Grant tries to force himself on Marcia but the escaping Gill Man breaks it up.
- Bittersweet Ending: The newly airbreathing creature walks into the ocean to try to return to his element after being rejected by humanity. He may drown unless his vaguely explained evolutionary ability saves him.
- Breaking the Bonds: When Gill Man wakes up after its surgery, it breaks the bonds on its hands and falls back to unconsciousness.
- Dirty Coward: When Barton murdered Grant, instead of accepting responsibility, he tries to stage a Frameup for the Gill Man to take the fall. When the Gill Man broke out, Barton attempts to run for his life like the squirming coward he is.
- Disney Villain Death: Barton dies when Gill Man throws him off from a balcony.
- Domestic Abuse: Barton is prone to emotionally terrorizing his wife.
- Evolutionary Levels: The titular creature as "the missing link" between man and fish, being a clawed, super strong, bipedal amphibious creature from the Paleozoic. They even try to "evolve" him into near human, and educate him. This ends badly.
- Crazy Jealous Guy: Barton. Seriously, this guy is a real piece of work.
- Frameup: After Barton kills Grant in an act jealous fury, he tries to put Grant's corpse into Gill Man's cage to frame it for the kill. This provides the catalyst for its escape.
- Harpoon Gun: When the creatures does its second attack on the boat, Grant shoots it with harpoons two times.
- Jerkass: Once again, Grant and Barton.
- Mad Scientist: Even if Gill Man wouldn't have burned, Dr. Barton had already plans of making it a land creature.
- Man on Fire: Gill Man is set on fire when it accidentally douses itself with gasoline and a lantern is thrown at it.
- Non-Malicious Monster: Gill Man is surgically changed into a land creature, and generally more humanlike. He's never a bad guy and befriends a woman and tries to protect her. All of which just puts him at odds with his own nature.
- Panthera Awesome: Random mountain lion jumps into Gill Man's cage and attacks the sheep. It then turns to Gill Man who kills it in self-defence.
- Scenery Porn: The underwater footage is just as pretty as in the first film.
- Sensor Suspense: Used when Dr. Morgan and others set to capture Gill Man on a boat.
- Sexy Silhouette: Shown when Marcia is undressing for a swim.
- Tragic Monster: The Gill Man is brutalized and mutilated by the main characters and in the end walks off to his death into the sea, the only place he ever considered to be his true home.
- Vader Breath: Gill Man's breathing when it is given lungs.
- Villain Protagonist: Crazy Jealous Guy Barton can be considered to be one (simply because the actor who played him received top billing). The Gill Man, who received more focus then the human characters this time, can count too, but more bordering on the Anti-Villain variety, though it's debatable if it's considered a villain, as unlike its previous appearances, the Gill Man does not do anything deliberately malicious at all in the film.