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- A-Virus
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- Aboleth (Pathfinder)
- Abomasnow
- Abomination (Marvel)
- Abomination (Mass Effect)
- Abra
- Absimiliard
- Abstract Daddy
- Abzorbaloff
- Achaierai
- Acid Breath
- Acklay
- Acromantula
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- Adamantine Golem
- Adjule (Resident Evil)
- Aegis VII
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- Aether
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- Aganos
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- Agito Makishima
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- Agwel
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- Albert Wesker (RE films)
- Albinoid
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- Alexis Hall
- Alfur
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- Alien (Skyline)
- Alien Beast
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- Alien Necromorph
- Alien Ships (Apocalypse)
- Alien Squid (Watchmen)
- Alpha Blogg
- Alpha Hopper
- Altamaha-ha
- AlterEgo
- Amalgam
- Amalgam Alpha
- Amarok
- Ambull
- Ammutseba
- Amon
- Amon-Gorloth
- Amon (Devilman)
- Ampulex Compressa Giganteus
- Amun
- Anakaris
- Anaxim
- AncientKazemon
- AncientMegatheriummon
- AncientMermaimon
- AncientSphinxmon
- AncientWisemon
- Ancient One (The Cabin in the Woods)
- Ancient Spirits of Evil
- Angel
- Angel (Dungeons & Dragons)
- Angel Star
- Angelique
- Angelo
- Angelos
- Angron
- Angry Bones
- Anguirus
- Ankheg
- Annastasjia
- Anole
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- Ansem
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- Anthony Fremont
- Anthropod
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- Antlion Grub
- Antlion Guard
- Antlion Guardian
- Antlion Soldier
- Antlion Worker
- Antlions (Terraria)
- Anubis (Resident Evil)
- Ao Oni
- Aphoom-Zhah
- Apollo
- Apollon
- Apotheosis
- Apsara
- Aptom
- Aqua Pirate
- Aqua Zebesian
- Aquatank
- Arachne
- Arachnid
- Aragog
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- Arcadia
- Arcanine
- Archanfel
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- Argus Panoptes
- Arkadimon
- Armadura
- Armaggon
- Armoured Knight
- Armus
- Arrowtongue
- Art the Clown
- Artemis
- Arwassa
- Asad
- Asanbosam
- Ash Clam
- Ashberry
- Ashigaru
- Ashley Fallon
- Ashrah
- Ashwinder (Cinzal)
- Asphyxia
- Astagoth the Devourer
- Astaroth
- Asteria
- Astraeus
- Astral Spirits (H.G. Wells)
- Astral Stalker
- Astro Zombie
- Asura
- Asylum Demon
- Athena
- Atlach-Nacha
- Atlas
- Atomic Flounder
- Atropal
- Audrey II
- Avatara
- Axe Man
- Axehandle Hound
- Ayi'ig
- Aylith
- Azathoth
- Azazel
- Azhorra-Tha
- Azog the Defiler
- Azrael (Dogma)
- B'gnu-Thun
- B.O.W.
- BFG
- Baal
- Baba Yaga
- Baba Yaga (folklore)
- Babai
- Babette
- Baboo
- Baby Dodongo
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- Babydmon
- Bad Juju
- Bagan
- Baker Family
- Baker Ranch
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- Balloon Boo
- Balrog
- Bandersnatch (Resident Evil)
- Bandit
- Banshee
- Banshee (Mass Effect)
- Baoht Z'uqqa-Mogg
- Baphomet (Cabal)
- Baragon
- Baraka
- Barbara Streisand (South Park)
- Barbas
- Barbie
- Barnacle
- Baron Samedi
- Barrel Spider
- Barroth
- Barrow-wight
- Barugon
- Basatan
- Basilisk
- Basilisk (Dark Souls)
- Bast
- Bastiladon
- Battle Cat
- Battle of Armageddon
- Battle of Canary Wharf
- Battleship
- Battra
- Beaman Monster
- Beast
- Beast (Marvel)
- Beast (SSSS)
- Beast Man
- Beast of Bodmin
- Beast of Bray Road
- Beast of Gévaudan
- Beast of the Land Between the Lakes
- Bebop
- Beedrill
- Beelzebub
- Beetle (Dungeon Keeper)
- Beetlejuice
- Behemoth
- Behemoth (Kingdom Hearts)
- Beholder
- Beldam
- Bell Gargoyles
- Bellsprout
- Belly Button Eater
- Beloit Motto
- Ben Tennyson
- Bendy
- Beowulf the Lightbeast
- Berk
- Bermuda Triangle
- Berserker (Nightbreed)
- Berserker Knight
- Berserker Lord
- Beyonder
- Bhlemphroim
- Bi Beast
- Big Blue
- Big Boo
- Big Mother
- Bigger Boo
- Bile Demon
- Bilfinger
- Bili ape
- Bill Cipher
- Billbo-Negg
- Billdad
- Billy Bob Goblin
- Bindi Bergara
- Bio-Freezer
- Bioconstruct
- Biolizard
- Biollante
- Bird Box Monster
- Bishamon
- Bit Sniper
- Biterfish
- Bitores Mendez
- Black Annis
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- Black Assassin
- Black Ballade
- Black Beast of Argh
- Black Bull
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- Black Death
- Black Doom
- Black Dragon
- Black Eyed Children
- Black Fog
- Black Fungus
- Black Hawk
- Black Knight
- Black Oak
- Black Tiger
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- Black Volt
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- Black Widow
- Black Wing
- Black Worm
- Blackness from the Stars
- Bladderhorn
- Blade
- Blade (Film version)
- Blastoise
- Blaze
- Blaze (Minecraft)
- Bloat
- Blob
- Blob (Resident Evil)
- Bloblet
- Blodeuwedd
- Blogg
- Bloggling
- Blood Crawler
- Blood Fiend
- Bloodletter
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- Bloodpack
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- Bloodshot (RE films)
- Bloodsucker (S.T.A.L.K.E.R.)
- Bloodsucker (Silent Hill)
- Bloodsucker (disambiguation)
- Bloodthirster
- Bloody Bones
- Bloody Mary
- Bloop
- Blot Toad
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- Blue Rhapsody
- Bluecap
- Bob
- Bob-omb
- Body Burner
- Bodyburster
- Bokoblin
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- Bolster
- Bomb Boo
- Bombshell Koopa
- Bommon
- Bone Eater
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