Cat, Great: Bekkah, Cheetah (AD&D Monster Manual II), Jaguar (AD&D Monster Manual), Lynx (AD&D Monster Manual), Spotted Lion (AD&D Monster Manual), Wildcat (AD&D Monster Manual II)
Dinosaur: Allosaurus (X1), Ankylosaurus (X1), Brontosaurus (X1), Titanothere (Expert rules, 1981), Tylosaurus (a type of Mosasaur, a larger version of the Mososaurus appearing in OD&D supplement II: Blackmoor and AD&D Monster Manual)
Dog: Normal (X9), War (AD&D Monster Manual; O2)
Eagle: Normal (AD&D Monster Manual II), Great (AD&D Monster Manual)
Eel: Electric (X7), Giant (X7), Weed (OD&D supplement II: Blackmoor)
Elk, Giant (X1)
Fish, Giant: Giant Catfish, Giant Piranha (Expert rules, 1981; subsequently appearing in X6)
Frog, Giant Poisonous (AD&D Monster Manual)
Gargantua (X7), similar to the Giant Gar (AD&D Monster Manual)
Hawk: Normal, Giant (Expert rules, 1981)
Lizard, Giant: Giant Foot-Pad Lizard (B10)
Magpie: Normal (a "friendly talking magpie" is mentioned in B2), Giant
Megatherium (X1)
Octopus, Giant (Expert rules, 1981; subsequently appearing in X7)
Owl, Giant (AD&D Monster Manual)
Oyster, Giant (X1, 1983)
Piranha (Cold-Water) (B10)
Porcupine, Giant (AD&D Monster Manual)
Raven & Crow: Normal, Large (AD&D Monster Manual II)
Rhinoceros: Normal, Wooly (Expert rules, 1981)
Shark: Vamora Shark
Skunk: Normal, Giant (AD&D Monster Manual)
Snake; Rock Rattler: Normal (B10), Giant
Squid, Giant (Expert rules, 1981; subsequently appearing in X7)
Conjurations:
Desert Ghost: Immature, Mature (similar to the Stormbiter from White Dwarf #19)
Faedorne (O2)
Fundamental: Air, Earth, Fire, Water (X8)
Gargoyle, Iron
Golem: Rock Golem, Silver Golem (similar to the AD&D Stone and Iron Golems)
Guardian Warrior & Horse: Warrior, Horse (likely based on the Terracotta Guardian from GameMaster Publications #1)
Homunculus: Ulzaq, Gretch, Fylgar (alignment-based, BECMI versions of the creature originally described in OD&D supplement I: Greyhawk)
Huptzeen (likely based on the Gem Hylem from TSR UK's Imagine Magazine #19)
Juggernaut: Stone, Wood (X4; subsequently appearing in X10; a special, small version appears in X8)
Kal-Muru (Ship Bane) (X8)
Living Statue: Silver, Rock/Ooze, Jade, Steel (B10)
Magen: Hypnos, Demos, Caldron, Galvan (X2; subsequently appearing in B12)
Nightmare (AD&D Monster Manual)
Reflecter
Silver Warrior (O2)
Soul Eater (X4; subsequently appearing in DA4)
Winged Warrior (B8)
Humanoids:
Bhut (X4) from "bhoot" a type of undead creature in Hindu mythology
Cay-Man (B6; subsequently appearing in X9)
Chameleon Man (B8) see also "The Land of Wallara" in Dragon #186
Crone of Chaos (B8)
Cryion (likely inspired by creatures named the Tran in Alan Dean Foster's 1974 novel "Icerigger". Details for the Tran were published in "GURPS Humanx: Roleplaying in Alan Dean Foster's "Humanx Commonwealth" by Steve Jackson Games in 1987.)
Dark Wing (similar to the Deep Glaurant from GAZ 8 "The Five Shires")
Elf, Aquatic (from OD&D supplement II: Blackmoor; subsequently appearing in PC3)
Flitterling (O2)
Garl (CM6; subsequently appearing in DA3)
Gator man (subsequently appearing in DA4)
Hephaeston (CM6)
Hutaakan: Priest, Warrior, Other (B10)
Kara-Kara (X8)
Kna (based on the Locathah from OD&D supplement II: Blackmoor)
Lupin (X2; subsequently appearing in X9) see also the "Kingdom of Renardy" in Dragon #179
Man, Isolated: Cynidiceans (B4), Quariks, Traldar: Warrior, Vocal, Other (B10)
Man, Primitive: Native (X1), "Wild Men" (including Pagans, originally described in X2), Barbarian
Oard (CM6)
Pachydermion (see "The Tower of the Elephant" by REH)
Phanaton (X1)
Rakasta (X1; subsequently appearing in X2) see also "The Kingdom of Bellayne" in Dragon #181
Rock Man (B8)
Shark-Kin (based on the Sahuagin from OD&D supplement II: Blackmoor; subsequently appearing in PC3)
Shargugh (O2)
Sis'thik (Desert Scourge) ride Xytars; similar to Sand Folk, subsequently appearing in DA3
Snapper (X9)
Sollux (X2) originally appeared as "Saraphs" (for AD&D) in an article by Tom Moldvay "Demons, Devils and Spirits" in Dragon #42; subsequently appearing in DA4
Stalwart
Tortle (X9)
Triton (from OD&D supplement I: Greyhawk; subsequently appearing in X7)
Wood Imp (subsequently appearing in PC1)
Lowlife:
Amber Lotus Flower (X2; subsequently appearing in X9)
Amoeba, Giant (X2; subsequently appearing in X9)
Archer Bush (B3)
Fyrsnaca (XS2)
Herex: Larva, Adult (subsequently appearing in DA3)
Jellyfish, Giant: Marauder, Man-O-War (X7)
Killer Tree (X2; subsequently appearing in X6) from Schick and Moldvay's "
Original Known World" campaign (see
this post); similar to the Hangman Tree in the AD&D Monster Manual II
Leviathan: Desert (similar to the Spice Worm from White Dwarf #17 (Feb/March 1980), Marine (similar to the Afanc in the AD&D Monster Manual II)
Masher (OD&D supplement II: Blackmoor)
Red Worm (XS2; subsequently appearing in B11)
Scorpion (Expert rules, 1981)
Serpentweed, Giant (X9)
Sirenflower (B6)
Slime Worm (X2)
Spider, Giant: Giant Hunting Spider (M2 "Maze of the Riddling Minotaur"; subsequently appearing in X6; B11), Giant Sand Spider (B8), Giant Shroud Spider (B10), Huge Wood Spider
Steam Weevil (B5) the stats for Steam Weevils and Piranha Birds were switched in the New Monsters section of B5, and the error was replicated for this entry but not Piranha Birds in AC9
Strangle Vine (X9) similar to the Choke Creeper in the AD&D Monster Manual II
Strangleweed (OD&D supplement II: Blackmoor)
Vampire Rose (B3; subsequently appearing in X2)
Whipweed (originally appearing in White Dwarf #9 (Oct/Nov 1978) as the Whipper; subsequently appearing as the Whipweed in the AD&D Fiend Folio)
Monsters:
Aranea (X1; subsequently appearing in X2) see also the "Magocracy of Herath" in Dragon #183
Ash Crawler (CM5)
Baldandar - see
The Baldanders in Jorge Luis Borges' "Book of Imaginary Beings"
Banshee, Lesser (B4)
Bargda (seemingly inspired by the Broo from Runequest/Glorantha)
Beetle, Earthquake (M2)
Beholder, Aquatic (similar to the Eye of the Deep from the AD&D Monster Manual)
Brain Collector (X2)
Chevall (B10)
Decapus: Land (B3) and Marine (X9)
Dragon, Sea (Expert Rules, 1981)
Dragonfly: White, Black, Green, Blue, Red (XL1)
Dragonne (AD&D Monster Manual; XL1; subsequently appearing in X9)
Dusanu (X5)
Fungoid (AC8)
Gakarak (subsequently appearing in DA3; DA4; "In Pursuit of the Slayer" from Dungeon #15 (Jan/Feb 1989)
Geonid (X5; subsequently appearing in DA3) seemingly inspired by the Garthim from "
The Dark Crystal" (1982)
Ghostly Horde (B8)
Grangeri (X1)
Gyerian (CM5)
The Hivebrood: Broodling, Hivebrood, Hiveleader, Broodmother, Hivemind (originally appearing in TSR UK's GameMaster Publications #1; subsequently appearing in "Of Nests and Nations" from Dungeon #13 (Sept/Oct 1988)
Hook Beast: Hook Horror (White Dwarf #12 (Apr/May 1979); AD&D Fiend Folio), Hulker (a weaker version of the Umber Hulk from OD&D supplement I: Greyhawk, without ability to confuse; XL1; subsequently appearing in DA3)
Hypnosnake (X3)
Ice Wolf (B10) similar to the Hound of Kerenos from White Dwarf #18 (Apr/May 1980); a slightly weaker, earlier version of the Quarg appearing in DA3)
Kopru (X1)
Kraken (AD&D Monster Manual II)
Lamara (characteristics of the Lamia from the AD&D Monster Manual, with the appearance of the Lamia Noble from the AD&D Fiend Folio)
Lava Lizard (B5; subsequently appearing in DA4)
Leveller (Bodendruker) see
The Leveler in Jorge Luis Borges' "Book of Imaginary Beings"
Pegataur (M2)
Phantom, Lesser (X2)
Phororhacos (X1)
Piranha Bird: Lesser (B5; subsequently appearing in X6), Greater
Pocket Dragon (M2 "Maze of the Riddling Minotaur"; subsequently appearing in X6)
Polymar (B4)
Randara (based on the Rakshasa from The Strategic Review #5; AD&D Monster Manual)
Roper (XL1; subsequently appearing in DA4)
Sabreclaw (CM3)
Scamille (similar to the Goom from White Dwarf #17)
Sea Horse (X7)
Sea Serpent: Lesser, Greater (X7)
Surtaki (could this creature be based on the Minotaur Lizard from OD&D supplement II: Blackmoor?)
Tabi (X4; subsequently appearing in X10)
Thunderhead
Water Weird (B7; subsequently appearing in B8)
White-Fang (similar to the Snow Serpent from Deities & Demigods)
Wychglow (similar to the Will o' Wisp from OD&D supplement I: Greyhawk)
Xytar (a slightly weaker, earlier version of the Camarilla appearing in DA3)
Yowler (similar to the Yeth Hound from the AD&D Monster Manual II)
Undead:
Agarat (X8)
Dark-Hood (Rorphyr)
Death Leech (CM2)
Dragon, Undead (similar to the Dracolich from "The Cult of the Dragon" in Dragon #110 (June 1986) although less powerful)
Elder Ghoul (mechanically similar to the AD&D ghast)
Grey Philosopher: Philosopher, Malice (subsequently appearing in "In Pursuit of the Slayer" from Dungeon #15 (Jan/Feb 1989)
Haunt, Lesser (B7)
Mesmer (similar to the Morkoth or Morlock from OD&D supplement II: Blackmoor)
Phygorax
Possession (subsequently appearing in "In Pursuit of the Slayer" from Dungeon #15 (Jan/Feb 1989)
Sacrol (M2 "Maze of the Riddling Minotaur"; subsequently appearing in X9; "In Pursuit of the Slayer" from Dungeon #15 (Jan/Feb 1989)*
*note the Sacrol is indicated with an asterisk in M2, indicating that silver, magic, or special weapons are needed to fight the creature (Cook/Marsh pg. X27). It's stated in X9 on pg. 22 that "When in combat with the sacrol, a magic weapon is needed to hit." although this is not explicitly stated in the creature description in AC9
Topi (X8)
Vapour Ghoul (XS2)
Velya (X7)
Wyrd: Normal, Greater (B10)