Shellycoat

​a shellycoat is a type of bogeyman that haunts rivers and streams.​ ​The name goes from the coat of shells these creatures are said to wear, which rattle upon movement.​ ​ Shellycoats are considered to be relatively harmless; they may mislead wanderers, particularly those they think are trespassing upon the creature's territory, but without malice. A common tactic of a shellycoat would be to cry out as if drowning and then laugh at the distracted victim.​

Amphibious in nature