Well, do you know how to build an animal from the inside out? If so then that should be a focus.

Really, good monsters come from knowing anatomy on existing animals.

There's sooo many. I would pick a theme or try and divide it into sections....even come up with a series maybe? That'd be neat, a whole series focusing on different species or origins... just an idea. Great concept though! I'd love to see some.

^this guy's got it covered. Since its a book about monsters, stray away from things that look too much like humans or too much like a single animal, as those topics have been covered by other sorts of how to draw books. Personally, I'd like to see a manananggal since I'm Filipino, or something like a manticore.

So here's a list of all the creatures and stuff I know of

A:
A Bao A Qu
Abada
Abaia
Abbagoochie
Abath
Abere
Abgal
Abraxa
Acephali
Achiyalabopa
Achlis
Acipenser
Acmonides
Actaeon
Adar Llwch Gwin
Adaro
Adjule
Adlet
Addonexus
Aegaeon
Aegir
Aello
Aenotherus
Aesir & Vanir
Aeternae
Afanc
Afrit
Agathos Daimon
Agloolik
Agog-Magog
Agta or Kapre
Agrippa
Agrius
Ahi
Ahuizhotl
Ai Tojon
Aicha Kandida
Aido Hwedo
Aigamuxa
Aillen Trechenn
Airavata
Akamataa
Akhekhu
Akhlut
Akki (Oni)
Akupara
Al
Alan
Albastor
Albion
Alchendic
Alcyoneus
Alecto
Alicanto
Aliens
Alifanfaron
Alkonost
Almas
Aloadae
Aloes
Alous
Alphito
Alphyn
Alsvid
Amal
Amarok
Ambize
Amduscias
Amermait
Amhuluk
A-mi-kuk
Amphithere
Amphisbaena
Anakim
Anaskelades
Anaye
Ancient One
Ancient Serpent
Androsphinx
Angboda
Angel
Angka
Angont
Ankou
Aniwye
Anjana
Anjing Ajak
Antaeus
Antero Vipunen
Anthropophagus
Antigonus
Antiphates
Antukai
Aonbarr
Apalala
Apep
Apis
Apocalyptic beasts
Apotamkin
Apotharni
Aranda
Arassas
Araxa
Araxa Junior
Arctophonos
Arepyiai
Arges
Argopelter
Argus
Aries
Arimaspi
Arimbi
Arion
Arrach
Arrak
Arusha/Arushi
Arzshenk
Ascapard
Asena
Ashuaps
Asin
Asipatra
Aspidochelone
Aspis
Asrai
Asterion
Astreus
Astrid
Astrope
Atcen
Athach
Atlas
Audumla
Aufhocker
Augerino
Aunyaina
Auvekoejak
Aswang
Axehandle Hound
Axex
Azeman
Azi Dahaka
Az-i-wu-gum-ki-mukh-'ti
Azrail
B:
Baba Yaga
Backoo
Bahamut
Bai Ze
Bakunawa
Balam
Banshee
Barbegazi
Bardi
Bar Juchne
Bartimaeus
Basilisk
Bastet
Batsu
Baykok
Behemoth
Beldan
Bergkonge
Bigfoot
Black Dogs
Local Variants
Blemmyae
Blob, The
Blurrs
Boggart
Bogie/Bogeyman
Bonnacon
Bray Road Beast
Brownie
Broxa
Buraq
Bysen
Bake-kujira
C:
Cacus
Calygreyhound
Calydonian Boar
Campacti
Canaima
Cana Hound
Capricorn
Catoblepas
Centaur
Centycore
Cercopes
Cerberus
Changeling
Chaneque
Chenoo
Cherubim
Charybdis
Chimaera
Chindi
Chitauli
Chupacabra
Ciguapa
Cipactli
Cretan Bull
Cruxim
Coblynau
Cockatrice
Coelacanth
Cyclops
Cynogriffon
D:
Death's-Head Hawkmoth
Dementor
Demon
Devalpa
Dhamphyr
Dip
Djinn
Dobhar-chu
Doppelgänger
Dragon
Ajatar
The Four Dragon Kings
Balaur
Bolla
Cuélebre
Dilong
Drac
Druk
DragonTurtle
Elux Lucis
Feathered Dragon/Serpent
Firedrake
Fucanglong
Gaasyendietha
Gargouille
Haietlik
Halowx
Imugi
Jaculus
Jiaolong
Knucker
Kulshedra
Li (Hornless dragon)
Lindworm
Long(Chinese)
Mizuchi
Niclumos
Odelete
Panlong
Peluda
Pi yao (Hybreed)
Pyrausta(Hybreed)
Python
Qiling (Hybreed)
Rainbow Serpent
Rồng
Ryū
Sea Weyvern
Shenlong
Sirrush
Tarasque
Tianlong
Yinglong
Drekavac
Dullahan
Dwarf
Dybbuk
Daeva
E:
Echidna
Elder
Elf
The Drow
Hugtandalfers
Night Elves
Rumpelstiltskin
Eli
F:
Fae
Sprite
Fairy
Father Time
Fearsome Critters
Fei Lian
Fenghuang
Fenris
Finfolk
Flying Fox
Four Horsemen of the Apocalypse
Frankenstein's Monster
Furies
G:
Gargoyle
Garuda
Gashadokuro
Genie
Ghidorah
Ghost
Ghoul
Giant
Gnome
Goat man
Goblin
Godzilla
Gorgon
Gog and Magog
Golem
Grant
Gremlin
Grendel
Griffin
Grim
Grim Reaper
Grither
Gugalanna
H:
Hadhayosh
Haetae/Xiezhi
Harpy
Haunt
Headless Horseman
Hell Hound
Hibagon
Hippalektryon
Hippogriff
Hobbit
Hoga
Hsigo
Huldra
Humbaba
Hydra
I:
Ibong Adarna
Imoogi
Itcuintlipotzotli
Imps
J:
Jabberwock
Jan
Jersey Devil
Jian
Jiang Shi
Jingwei
Jormungand
Jotnar/Jotunn
Jumpity-Jim
K:
Kalanoro
Kampe
Kappa
Kelpie
Keythong (Alce)
Kirin/Qilin
Knocker
Kraken
Krusnik
Kitsune
L:
Ladon
Lamasu
Lamia
Lectoblix
Leprechaun
Leviathan
Lich
Lilith
Lilim
Loch Ness Monster
Lorelei
Loup Garou
Loveland Frog
Lucifer
M:
Magnathorax
Mahisha
Mammon
Manananggal
Manticore
Medusa
Megalodon
Menehune
Merfolk (Merbeings)
Mermaid
Merrow
Minotaur
Mishipeshu
Mngwa
Mongolian Death Worm
Montauk Monster
Mother Nature
Mothman
Mothman Sightings
Mothra
Mummy
N:
Naga
Nagual
Naiad
Narasimha
Narcoblix
N-dam-keno-wet
Neko
Nine-headed Bird
Ningyo
Nøkken(Puken)
Nuckelavee
Nymph
O:
Opinicus
Oracle
Orfeo Shifter
Otherkin
Ouroboros
P:
Pegasus
Peng
Peryton
Phoenix
Phooka/Puck
Pixie
Poltergeist
Q:
Quanlier
Quetzalcoatl
Quotote
R:
Ratman of Southend
Raven
Ravenmocker
Reaper
Redcap
Red Dragon (Draig Coch)
Roc (Ruhk)
Rodan
Rods
Rui Shi/Too Jou Shen
S:
Sandman
Satyr
Sceadugenga
Scylla
Sea Serpent
Selkie
Sennin
Seraphim
Seveocha
Shadow People
Shishi
Sidhe
Six Legged Salamander
Sigbin
Siren
Skinwalker
Slender Man
Sphinx
SpringheeledJack
Striga
Succubus
Syragh
T:
Taniwha
Tarasque
Tengu
Tetramorph
Thestral
Thunderbird
Tiamat
Tikbalang
Tikoloshe
Titan
Tiyanak
Tlatecuhtli
Treefolk
Apple Tree Man
Ent
Green Man
Willow Man
Troll
Trunko
Typhon
U:
Undine
Unicorns
V:
Vampire
Psionic Vampire
Strigoii
incomplete vampires research. by shirimasen
Vampire Origins
Valkyrie
W:
Warlock
Water Leaper
Wendigo
Werewolf
Western Dragon
White Eyes
Will 'o' Wisp
Wraith
Wyvern
X / Y / Z:
Xolotl
Yanluo
Yeti
Yggdrasil
Yokai
Kamaitachi
Kitsune
Tsukumogami
Yowie
Yurei
Zaratan
Zhulong (Hybrid)
Ziz
Zombie