But due to mishandling, the room is left open and the section begins to thaw, only for scientists to find that it is starting to regenerate.

Professor Otto 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 planarians and starfishs.

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).

The monster is finally rendered unconscious by a sedative developed by ingenious scientists and shot into its mouth from a bazooka fired by General Grayson.

Facilities in Denmark, by Hollywood standards, are notably lacking; but fine craftsmen who put everything together by hand are not concerned with the time it takes, (and) are excellent".

Pink also said "the Scandinavian countries have never truly been exploited by Hollywood filmmakers, so the settings have remained unusually fresh ground for motion pictures.

[13] In July 2024, it was released as 4K Blu-ray from Vinegar Syndrome, with Poul Bang's Danish-language Reptilicus included among several bonus-features in this three-disc set.

"[15] Describing the film as a "hilarious sci-fi mess," critic Hans Wollstein further noted in AllMovie that it "contains filmdom's perhaps least convincing monster and some of the worst performances imaginable," that "Ottosen's wooden performance is second only to that of Bodil Miller, a former Universal starlet who appears here for no apparent reason," and "a low point of the film is pop star Birthe Wilke's rendition of a ditty, 'Tivoli Nights', to a visibly dazed audience.

[19] Writing in DVD Talk about Scream Factory's Blu-ray release, Kurt Dahlke reported that "Reptilicus seems aimed squarely at the monster kids in the audience," that no viewers "will concern themselves with the plot," and that "Special Effects are not this movie's strong point, but they are its selling point," with a monster that "often slithers about slowly, like an arthritic hand-puppet.

"[20] Reviewing the same release, Matt Brunson from Creative Loafing also gave the film a negative review: "The effects used to create Reptilicus (a puppet, basically) are no worse than those seen in many of the era's films (it still beats the oversized bird in The Giant Claw, for starters), but the effects employed when the creature does something like munch on humans or shoot acidic green slime from its mouth manage to travel beyond atrocious.

[...] Awkward dubbing of foreign actors, special effects that look like they cost a buck fifty, laughably earnest dialogue, wince-inducing comic relief from a dim-witted character — if ever a movie was made that deserved to be showcased on the cult series Mystery Science Theater 3000 it's this one".

[25] In 2020, PS Artbooks published the two issues of Reptilicus as a bonus in the first two volumes of their Kona, Monarch of Monster Isle trade paperback series.

On April 25, 2010, Reptilicus was performed as an experimental stage play at Skuespilhusets Portscene in central Copenhagen, a co-production between Eventministeriet and CPH PIX.