Villain(s)  Shapeless mass

Actor(s):  John Merivale, Didi Perego, Gérard Herter, Giacomo Rossi-Stuart

Brief Description  Caltiki – The Immortal Monster (Caltiki, il mostro immortale) is a 1959 Italian horror-sci-fi film directed by Riccardo Freda and uncredited co-director/cinematographer Mario Bava. It follows a team of archaeologists in Mexico who discover a deadly, flesh-dissolving protoplasmic creature linked to the collapse of the Mayan civilization.

Plot:
In Mexico, a team of archaeologists led by Prof. John Fielding (John Merivale) investigates a deserted ancient Mayan city to uncover why the civilization vanished overnight in 607 AD. After a delirious team member stumbles back into camp, the scientists head down into an underground grotto. They locate a massive statue of the sacrificial goddess Caltiki, guarding a deep, radioactive pool. A diver enters the pool to salvage ancient gold treasure. When his crew pulls him back up, they find his flesh entirely dissolved down to the bone. A massive, flesh-eating protoplasmic blob then rises from the pool.

The monster aggressively latches onto the arm of an unlikable team member, Max Gunther (Gérard Herter). While Fielding manages to hack the monster away with a machete and destroy the bulk of it using fire, a small fragment of the creature remains permanently fused to Max's arm. Back in a laboratory, the fragment slowly eats away at Max's flesh and infects his mind, driving him into a mad, murderous frenzy. Meanwhile, Fielding studies a separate isolated tissue sample of the creature.

Fielding discovers that Caltiki is a unicellular prehistoric organism that expands exponentially when exposed to cosmic radiation. Coincidentally, a radioactive comet that passes Earth once every few thousand years—the exact comet that originally caused the destruction of the Mayans—is returning. As the comet arrives, the sample in Fielding's home rapidly multiplies into a house-sized leviathan, trapping his family inside. Fielding calls upon the Mexican military, who finally manage to incinerate the immortal beast using flamethrowers.