Lethifold

The Lethifold (also known as Living Shroud) is a carnivorous and highly dangerous magical creature. Its appearance resembles that of a black cloak that is half an inch thick, though thicker if the Lethifold has recently digested a victim. It glides along the ground and other surfaces in an unknown form of locomotion in search of its prey, humans. It attacks its prey at nighttime, when the target is asleep, and suffocates and digests it there and then.

There has been only one known survivor of a Lethifold attack, a certain Flavius Belby, who managed to escape because he was not fully asleep at the time. He repelled the Lethifold with a Patronus Charm 1, something other people are unable to do because they are either asleep or Muggles (or both). Kicking may be of some use in tight spots.

Thankfully, the Lethifold is a very rare species, and can only be found in the tropics.