From the Fog Map for MCPE

When a thick fog envelops the mcpe world, there are Creatures of the Fog who are mysterious entities that inhabit the areas covered by the thick fog. It is said that they are nature spirits that reside among the layers of fog, appearing only to those who dare to explore the darkness and mystery of nature. Players who dare to explore the area covered by the fog will be faced with the presence of the Creatures of the Fog. Their forms resemble shadows moving amongst the mist, giving the impression that they are part of a larger universe. Not much is known about the Creatures of the Mist, other than that their presence often marks the existence of ancient places full of hidden secrets. Some say that they are nature's guardians who protect forests and lands covered in thick fog.

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