Abyssal Sea Monster Life and Death Duel

A flooded underground megastructure, ancient stone corridors half-submerged in black water, bioluminescent algae pulsing like a heartbeat along the walls. A masked diver, wearing worn tactical gear, illuminated by a flickering flare on her wrist. She is dragged down by a powerful undertow generated by a massive eyeless sea beast moving beneath the floor grates, through collapsing flooded chambers. The camera follows closely behind the diver, water rushing past broken stone arches, bubbles and debris spiraling past the lens. The diver grabs a broken column to steady herself, the current tearing at her body, then she lets go, free-falling into a vertical shaft, twisting to dodge the translucent tentacles of the sea beast whipping upwards in the darkness. A fast-shaking camera captures her igniting a harpoon gun while falling, the flare illuminating the creature's massive gaping jaws below. In the final motion, the camera spirals down around her as she fires the harpoon into the creature's mouth, bioluminescence erupting into a blinding white light, the camera breaks through the surface of a vast underground ocean, the diver's silhouette silhouetted against the light of thousands of pulsing creatures on the ceiling of a cathedral-sized cavern. 15 seconds.