Hag
Female magical beings, less human-like than witches (PA4) They are wild in appearance. They have been known to eat children (FB), although at the Leaky Cauldron a hag ate raw liver (PA4). They can be quite frightening, apparently, since Quirrell had a "nasty bit of business" with one during his year off for first-hand experience in fighting the Dark Arts (SS5). Hags are not as adept as wizards at disguising themselves (GF19)

Hellhound
Muggle name for the three-headed dog who according to their mythology guards the gates of Hades. The dog's name was Cerberus. Hagrid had a huge three-headed dog which he called Fluffy. (SS

Hinkypunk (PA9) 
The Hinkypunk is a little one-legged creature, looking as though it were made of smoke. The Hinkypunk carries a light with which it lures travelers into bogs.

Hippocampus
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A Hippocampus is a Mer-horse, with the head and forequarters of a horse and the hindquarters and tail of a giant fish (FB).

Hippogriff (PA6)
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The Hippogriff is a stange flying creature with the head of an eagle and the body of a horse. Hippogriffs are extremely dangerous until they are tamed, which should only be attempted by trained wizards. A person wishing to approach a Hippogriff should bow first; if the animal bows in return, it can be touched and even ridden. 
Hagrid had a Hippogriff named Buckbeak which was nearly executed for injuring Draco Malfoy. Buckbeak was freed and Sirius Black rode him as they both escaped (PA, FB)

Horklump
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The Horklump is a rather pesky creature which resembles a pinkish mushroom covered with bristles. Horklumps are considered a garden pest. They are the favorite food of Gnomes. (FB

Horned Toad (GF14)
Neville had to disembowel an entire barrel full of horned toads for Snape's detention.

horse, winged
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Twelve palomino horses the size of elephants pull the Beauxbatons carriage as it flies through the sky. These magnificent animals are very powerful and require forceful handling. They drink only single-malt whiskey (GF15)

There are several breeds of Winged Horses:

• Abraxan - powerful, giant Palominos (probably what pulled the Beauxbatons carriage)
• Aethonan - chestnut, popular in Britain and Ireland
• Granian - grey, fast
• Thestral - black, can become invisible, considered unlucky

human-like creatures
Creatures which look like normal human beings but which are not, (at least some of the time in the case of werewolves)

• hags
• vampires
• werewolves

insects
and insect-like creatures

• Billywig
• Glumbumble
• lacewing flies
• Chizpurfle

Jarvey
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Resembling an overgrown ferret, the Jarvey is one of the few beasts which can actually talk. It's speech, however, consists entirely of rude phrases and insults. Jarveys chase Gnomes.

Jobberknoll
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The Jobberknoll is a tiny blue speckled bird which makes no sound until the moment of its death, when it lets out a long scream consisting of all the sounds it has ever heard. (FB)

Kappa
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Water-dwellers who look like scaly monkeys with webbed hands, Kappas will grab and strangle waders in their ponds (PA8)
According to Snape, the Kappa is commonly found in Mongolia (PA9), but the textbook states that the Kappa is a Japanese creature (FB).
web link

Kelpie
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Lockhart advises Hagrid how to get these out of the well (CS7)
The world's biggest Kelpie is the Loch Ness Monster (FB).
web link

Knarl
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Very similar to a hedgehog, except that the Knarl takes offense easily and will wreak havoc on garden plants. (FB)

Kneazle (NEE-zul)
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Cat-like creature, very intelligent. The Kneazle can detect unsavory or suspicious persons very well and will react badly to them. However, if it takes a liking to a Witch or Wizard, it makes an excellent pet (FB). The Kneazle has spotted fur, large ears, and a lion-like tail.
Crookshanks is part Kneazle (Nr).

Lacewing Fly
These insects are used as potion ingredients. They are small insects with large, transparent wings. Lacewing flies eat aphids. (CS 
web link

Leech
A small slug-like creature that lives in water. Leeches attach themselves to other creatures and suck their blood. Leeches are used as potion ingredients, both sliced and in the form of Leech Juice.
web link

Leprechaun
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Leprechauns are tiny creatures which look like little green humans. They can speak, although they are not classified as "beings." Leprechauns eat leaves.
Leprechauns are the Irish National Quidditch Team's mascots (GF
Leprechauns produce a gold-like substance which vanishes after an hour or two (GF

Lethifold
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This dangerous beast resembles a half-inch thick black cloak which moves along the ground at night, hunting its prey. It attacks sleeping humans, smothers them, and then digests them, all in their bed, leaving no trace at all. The only defense against a Lethifold is a Patronus Charm. Thankfully, this frightening creature is rare, only found in the tropics. (FB)

Liondragon
The Chinese Fireball dragon is sometimes known by this name. (FB)

Lobalug
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Sea creature which consists of a poison sac and a spout. The Lobalug is used as a weapon by Merpeople (FB).

Mackled Malaclaw
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The Malaclaw is a creature of the shore and coastline. It resembles a lobster.The Malaclaw's bite gives the victim bad luck for up to a week (FB).

Manticore
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This terrifying beast has the body of a lion and the head of a man. It's tail is that of a scorpion. The Manticore originated in Greece. 
In 1296, a Manticore seriously wounded someone but was let off because no one dared go near it. (PA11). 
Hagrid bred the Blast-Ended Skrewt from a Manticore and a Fire-Crab. (GF24)
web link

Merpeople
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Sentient beings which live underwater in villages at the bottom of lakes and seas. Merpeople speak Mermish, a language which sounds like a horrible screeching noise but which is understandable underwater. The Merfolk who live in the Lake near Hogwarts are led by Merchiefteness Murcus. (GF25)
In 1949, the Merpeople caught a Hippocampus off the coast of Scotland and domesticated it. (FB)
Merpeople are also known as Sirens (Greece), Selkies (Scotland), and Merrows (Ireland). (FB)
Merpeople sometimes use Lobalugs as weapons. (FB)

Merrow
A Merrow is a Merperson from the lakes and seas of Ireland (FB).

Moke
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The Moke is a small lizard which can shrink at will. (FB)

Mooncalf
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The Mooncalf is a strange creature that lives in a burrow. It only comes out at the full moon when it dances on its enormous flat feet, sometimes leaving intricate patterns in wheatfields (much to the confusion of Muggles). The silvery dung of the Mooncalf, if collected before the sun comes up, makes an excellent fertilizer. (FB)

Mosag
A female Acromantula, mate of Aragog. Currently living in the Forbidden Forest near Hogwarts (CS.

Mountain Troll
SEE Troll

Mummy
(PA7)
A mummy is a frightening creature, possibly a manifestation of a Curse left behind by ancient Egyptian wizards. Actual mummies are the presernved remains of deceased people of ancient Egypt. It is unclear whether the type of Mummy Parvati Patil fears (which the Boggart impersonates during Defense Against the Dark Arts class with Lupin), bandaged, bloody, and sightless, is an actual mummy animated or some Dark Creature which resembles a Mummy.
web link about mummy curses

Murtlap
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The Murtlap is a rodent which lives along the seashore. On its back is a growth resembling a sea anemone which when eaten can promote resistance to curses. The Murtlap will attack anyone who steps on it, although it usually eats crustaceans, not people's feet (FB).