These creatures were listed in "Fantastic Beasts and Where to Find them" and from the HP series. The M.O.M. Rating shows how dangerous it is.
Acromantula
M.O.M Rating: XXX
Ashwinder
M.O.M Rating: XXX
Augurey
M.O.M Rating: XX
Basilisk
M.O.M Rating: XXXXX
Billywig
M.O.M Rating: XXX
Bowtruckle
M.O.M Rating: XX
Bundimun
M.O.M Rating: XXX
Boggart
M.O.M. Rating: Unknown
Centaur
M.O.M Rating: XXXXX
Chimaera
M.O.M Rating: XXXXX
Chizpurfle
M.O.M Rating: XXX
Clabbert
M.O.M Rating: XX
Crup
M.O.M Rating: XXX
Demiguise
M.O.M Rating: XXXX
Dementor
M.O.M. Rating: Unknown (Probably XXXXX)
Diricawl
M.O.M Rating: XX
Doxy
M.O.M Rating: XXX
Dragon
M.O.M Rating: XXXXX
Dugbog
M.O.M Rating: XXX
Erkling
M.O.M Rating: XXXX
Erumpent
M.O.M Rating: XXXX
Fairy
M.O.M Rating: XX
Fire-Crab
M.O.M Rating: XXX
Flobberworm
M.O.M Rating: X
Fwooper
M.O.M Rating: XXX
Ghoul
M.O.M Rating: XX
Glumbumble
M.O.M Rating: XXX
Gnome
M.O.M Rating: XX
Graphorn
M.O.M Rating: XXXX
Griffin
M.O.M Rating: XXXX
Grindylow
M.O.M Rating: XX
Hippocampus
M.O.M Rating: XXX
Hippogriff
M.O.M Rating: XXX
Horklump
M.O.M Rating: X
Horse,
Winged
M.O.M Rating: XX - XXXX
Imp
M.O.M Rating: XX
Jarvey
M.O.M Rating: XXX
Jobberknoll
M.O.M Rating: XX
Kappa
M.O.M Rating: XXXX
Kelpie
M.O.M Rating: XXXX
Knarl
M.O.M Rating: XXX
Kneazle
M.O.M Rating: XXX
Leprechaun
M.O.M Rating: XXX
Lethifold
M.O.M Rating: XXXXX
Lobalug
M.O.M Rating: XXX
Mackled
Malaclaw
M.O.M Rating: XXX
Manticore
M.O.M Rating: XXXXX
Merpeople
M.O.M Rating: XXXX
Moke
M.O.M Rating: XXX
Mooncalf
M.O.M Rating: XX
Murtlap
M.O.M Rating: XXX
Niffler
M.O.M Rating: XXX
Nogtail
M.O.M Rating: XXX
Nundu
M.O.M Rating: XXXXX
Occamy
M.O.M Rating: XXXX
Owl
M.O.M. Rating: Unknown (Probably X or XX)
Phoenix
M.O.M Rating: XXXX
Pixie
M.O.M Rating: XXX
Plimpy
M.O.M Rating: XXX
Pogrebin
M.O.M Rating: XXX
Porlock
M.O.M Rating: XX
Puffskein
M.O.M Rating: XX
Quintaped
M.O.M Rating: XXXXX
Rabbit
M.O.M. Rating: Unknown
Rat
M.O.M. Rating: Unkown
Red Cap
M.O.M Rating: XXX
Salamander
M.O.M Rating: XXX
Snidget
M.O.M. Rating: XXXX (because there are severe penalties if one is injured or captured)
Sphinx
M.O.M. Rating: XXXX
Streeler
M.O.M Rating: XXX
Tebo
M.O.M. Rating: XXXX
Troll
M.O.M. Rating: XXXX
Unicorn
M.O.M. Rating: XXXX
Vampire
M.O.M. Rating: Unknown (Probably XXXX)
Veela
M.O.M. Rating: Unknown
Werewolf
M.O.M. Rating: XXXXX
Wood Nymph
M.O.M. Rating: Unknown
Yeti
M.O.M. Rating: XXXX