Muggles' Guide to Harry Potter/Magic/Hinkypunk

Overview
A Hinkypunk is a small, one legged creature that appears to be made out of smoke. It carries a lantern that is used to lure unsuspecting travelers into bogs.

Extended Description
The term is first introduced in Harry Potter and the Prisoner of Azkaban. When Professor Snape substitutes for Professor Lupin in Defense Against the Dark Arts, he instructs the class to turn to the section on Werewolves; Hermione protests "We're due to start hinkypunks."

Later in the year Professor Lupin sets up an obstacle course for the third years' final exam. One of the obstacles is to "squish their way across a patch of marsh while ignoring misleading directions from a hinkypunk."