Resembling a giant dragon-like serpent with webbed wings, Reptilicus, with near-impenetrable armor-plated skin, had the ability to regenerate itself from any segment as well as fly (a feature obscured in the US version, when AIP removed the flying scene). In the US version, an effect was added (albeit randomly and clumsily) where Reptilicus shot a neon-green acid slime from his mouth.
The special effect used to bring Reptilicus to life is a wired marionette.
Danish miners dig up a section of a giant reptile's tail from the frozen grounds in Lapland, where they are drilling. The section is flown to the Danish Aquarium in Copenhagen, where it is preserved in a cold room for scientific study. But due to careless mishandling, the room is left open and the section begins to thaw, only for scientists to find that it is starting to regenerate.
Professor Martens, who is in charge of the Aquarium, dubs the reptilian species "Reptilicus" (upon a reporter's suggestion) and compares its regeneration abilities to that of other animals like earthworms and starfish.
Once fully regenerated from the tail section, Reptilicus goes on an unstoppable rampage from the Danish countryside to the panic-stricken streets of Copenhagen (including one of its famous landmarks, Langebro Bridge), before finally being killed with poison by ingenious scientists and military officers.
However, the monster's foot is not destroyed and sinks to the bottom of the sea. The movie is left open-ended, with the possibility that the foot could regenerate.