A gremlin can traverse water. It is humanoid. It is poisonous if eaten.

The gremlin is a highly intelligent and completely evil creature. It lives to torment other creatures and will go to great lengths to inflict pain or cause injury. Suddenly, Wilson thought about war, about the newspaper stories which recounted the alleged existence of creatures in the sky who plagued the Allied pilots in their duties. They called them gremlins, he remembered. Were there, actually, such beings? Did they, truly, exist up here, never falling, riding on the wind, apparently of bulk and weight, yet impervious to gravity?
He was thinking that when the man appeared again.
Nightmare at 20,000 Feet, by Richard Matheson