Ampatta/Demonter: Mummies that periodically drain the life out of an unwilling victim with a deadly kiss.

Bogart: Harmless creature that tries to scare you by changing into something you are afraid of.

Centuar:
M.O.M classification: XXXX      Half horse, half human. Very intelligent an capable of speech.

Collectors: Warlocks that steal information from people's minds with mind control.

Congi: Has the power to steal power from other demons, and the life-forces from mortals.

Dragons:
M.O.M classification: XXXXX   Normally big creatures who usually breathe fire. Dragons have many magical properties. There are ten breeds of dradon, though these have been known to interbreed on occasion, producing rare hybrids. pure-bread dragons are as follows:  Antipodean Opaleye, Chinese Fireball, Common Welsh Green, Hebridean Black, Hungarian Horntail, Norwegian Ridgeback, Peruvian Vipertooth, Romanian Longhorn, Swedich Short-Snout and Ukrainian Ironbelly.

Eyghon: An acient demon who lives by posessing the souls of dead or unconscious people.

Fire Lizard: kind of a baby dragon, enjoys playing in fire.

Flobberworm:
M.O.M classification: X   worm that eats lettuce. Sometimes used to thicken potions.

Gentleman: Come to a town & steal the voices of the townspeople. Then go into their houses and steal their hearts. They need 7 to gain ultimate power. They only can be killed by the scream of a witch.

Giant Squid: A giant, octopus like creature, lives in large bodies of water, such as the lake at Hogwarts.

Gnomes:
M.O.M classification: XX The gnome a common garden pest found throughout northern Europe and North America. It may reach a foot in height, with a disproportionately large head and hard, bony feet. 

Hinkypunk: a one legged creature that appears to be made of wisps of smoke, it lures travelers into bogs.

Hippogriff:
M.O.M classification: XXX Half horse, half bird.

House elves: Creatures with long, pointy bat like ears that live in homes and are happy servants to their masters. (excluding Dobby)

Kappas:
M.O.M classification: XXXX  Water dwellers, look like scaly monkeys, they have webbed hands and they strangle people who are swimming, usually from Mongolia.

Machida: A huge snake demon that arises each year and eats 3 women that are led by demons and are transformed into frat boys who gain power after every death.

Mage: Are Special people that have powers that come in different areas: craftmaking, weather and plants.

Mareners: Sea fairies.

Mer-people:
M.O.M classification: XXXX Water creatures whose top halves of their body are human, and the bottom halves resemble fish. They can't survive on land.

Pegasus: flying horse.

Phoenix:
M.O.M classification: XXXX  A bird that rises from the ashes and has healing tears.

Red Caps:
M.O.M classification: XXX  Dawarf-like, they stay where there was once bloodshed, waiting to attack people who are going to ransack the site.

Unicorns: M.O.M classification: XXXX   Horse-like creatures that can be any color that have a horn coming out of its forehead. Most have wings. Seems to like witches more than wizards

Warlocks: They come in all different sizes, their main concern is evil. Warlock means TruthTwister.
Some of the below have a M.O.B (Ministry of Magic) classification:

XXXXX              Known wizard killer / impossible to train or domesticate

XXXX                Dangerous / requires specialist knowledge / skilled wizard may handle

XXX                  Competent wizard should cope

XX                     Harmless / may be domesticated

X                        Boring

For more information see Fantastic Beasts & Where To Find Them (By Newt Scamander)
Magical Creatures