Poseidoceros' are fish, mutated by radiation, that have grown to unnatural size. Their physiology has dramatically altered through the two centuries of magical radiation in Soft Swell Lake. A Poseidoceros is almost crustacean in its exoskeleton, with thick, prominent scales covering their entire body, including their faces. It is impossible to determine, short of dissection, whether or not they have eyes at all, as they are shown to be non-senstive to light. In addition to their scales, they bear protruding, trident-like teeth, sharp enough to gore smaller creatures, which includes ponies, should they ever venture beneath the surface.