"Mysterious Fog" is episode 240 of the Berserk manga series.
Synopsis[]
Guts, Serpico and Isidro are hard at work defending Schierke, Farnese, Casca and the young black-haired boy from the crocodiles. As he fights, Guts begins to feel the Beast of Darkness' influence creep into his mind, but manages to keep it at bay by only drawing on a fraction of the Berserker Armor's power.
One of the crocodiles manages to get dangerously close to the shack, having slipped by the three fighters outside. Schierke is indisposed as she is in the middle of a magic ritual, so the frightened Farnese takes it upon herself to defend the witch, Casca and the boy. She draws her dagger. This act alone seems to deter the crocodile from entering the cabin, and it moves away. Nobody is aware that, only moments before the crocodile turned away, it made eye contact with the small boy.
Schierke completes her ritual, raising a bulwark around the cabin and summoning the familiar four-hued pillar of light which, at night, resembles an aurora. She then mentally calls out to Guts, Serpico and Isidro, explaining that while the bulwark is slightly effective against the crocodiles due to their being possessed by Astral entities, the crocodiles themselves still possess bodies of the physical world, and are thus capable of bypassing the bulwark's barrier.
The combination of the full moon and Guts' using the Berserker Armor allows the Beast of Darkness to take over Guts' mind very easily.
While the three men continue fighting, Schierke begins a mental search of the area to find out who is controlling the crocodiles. During this time, the Beast of Darkness slips ever more into Guts' mind, and the wolf's head helmet of the Berserker Armor begins to manifest. He telepathically calls out to Schierke to hurry her search, though this proves to be unneeded: Serpico has managed to locate the magic users responsible for controlling the crocodiles, four harashada, or Kushan monks, and beheads them all with a single swipe of his sylph sword. The moment the harashada die, the crocodiles return to their true nature, dropping their weapons and walking on all fours back to the ocean.
Despite the crocodiles having left, Schierke senses that the fight isn't over. Serpico looks down at the severed heads of the harashada and notices that a strange fog is flowing out of their mouths and noses; the fog expands and forms a human-like face before fading. Suddenly, a massive beast rises out of the ocean a short distance away from Serpico, who rushes back to the cabin and warns everyone that they must flee.
However, the group is too distracted by the horrific creature that follows right behind Serpico - a massive beast, a demonic cross between a whale and an elephant that uses its fins to drag itself along the beach.