The following lists group all of the monsters in this book into their respective terrains. Note that there can be a certain amount of crossover on these lists, especially between climate bands, similar terrains, or a planar terrain and the Materal Plane. For example, although behirs are normally encountered in warm deserts, it's certainly possible to encounter one in a temperate desert (but much less likely to find one in a cold desert). Likewise, while bulettes usually limit their hunts to hilly terrain, it wouldn't be unusual to find one in the mountains or even on a plain. Creatures listed under planar terrains can usually be encountered anywhere on the Material Plane as well, but are only very rarely encountered on planes other than the one associated with them. In short, use these lists as a guide, not as shackles—if your adventure works better with a sphinx encountered in a cold forest, by all means, go for it! Just keep in mind that you should also probably come up with an in-game reason to explain the monster's presence there.
Any Terrain
animated object, barghest, basilisk, clay golem, devourer, dog, doppelganger, fire beetle, flesh golem, gargoyle, ghost, ghoul, giant ant, giant spider, greater barghest, greater shadow, hell hound, homunculus, iron cobra, iron golem, kyton, lich, mimic, minotaur, mohrg, mummy, nessian warhound, rakshasa, rat swarm, riding dog, shadow, skeletal champion, skeleton, spectre, spider swarm, stone golem, tarrasque, vampire, vargouille, werewolf, wight, wood golem, wraith, xill, yeth hound, zombie
Any Terrain (Cold)
Any Terrain (Temperate)
cyclops, bat swarm, dire bat, lizard, rat, venomous snake
Any Terrain (Warm)
army ants, bat swarm, cyclops, dire bat, lizard, storm giant, venomous snake
Coastline
bronze dragon, crab swarm, giant crab, pteranodon
Desert (cold)
Desert (Temperate)
Desert (Warm)
bat, behir, blue dragon, brass dragon, giant scorpion, gnoll, janni, phoenix, sphinx
Forest (Cold)
dire bear, dire tiger, dire wolf, dire wolverine, grizzly bear, mastodon, tiger, treant, winter wolf, wolf, wolverine
Forest (Temperate)
assassin vine, bat, boar, centaur, dire boar, dire tiger, dire wolf, dryad, ettercap, giant mantis, giant scorpion, giant stag beetle, giant wasp, goblin, goblin dog, green dragon, half-celestial unicorn, hawk, kobold, nymph, owl, owlbear, pixie, pseudodragon, satyr, shambling mound, tiger, toad, treant, unicorn, wasp swarm, wolf, worg, yellow musk creeper
Forest (Warm)
ankylosaurus, bat, boar, brachiosaurus, centipede swarm, constrictor snake, couatl, deinonychus, dire ape, dire boar, dire tiger, giant centipede, giant frilled lizard, girallon, gorilla, leopard, monitor lizard, monkey, tiger, toad, treant, tyrannosaurus, yellow musk creeper
Rivers/Lakes
aboleth, constrictor snake, crocodile, dire crocodile, electric eel
Hills (Cold)
crag linnorm, ettin, ice linnorm, ogre, ogre mage
Hills (Temperate)
bulette, chimera, gorgon, griffon, hill giant, hobgoblin, ogre, orc, weasel, wyvern
Hills (Warm)
behir, copper dragon, dire lion, giant frilled lizard, manticore, phase spider, phoenix, sphinx, wyvern
Mountains (Cold)
frost giant, ice linnorm, troll, yeti, white dragon
Mountains (Temperate)
bugbear, cloud giant, eagle, giant eagle, orc, silver dragon, tengu
Mountains (Warm)
Ocean (Cold)
aboleth, crab swarm, dire shark, dolphin, giant crab, giant octopus, giant squid, kraken, octopus, orca, sea hag, sea serpent, shark, shoggoth, skum, squid
Ocean (Temperate)
aboleth, crab swarm, dire shark, dolphin, dragon turtle, giant crab, giant octopus, giant squid, kraken, merfolk, octopus, sahuagin, sea hag, sea serpent, shark, skum, squid
Ocean (Warm)
aboleth, crab swarm, dire crocodile, dire shark, dolphin, elasmosaurus, giant crab, giant moray eel, giant octopus, giant squid, kraken, sahuagin, sea hag, sea serpent, shark, squid
Plains (Cold)
bison, dire tiger, mastodon, winter wolf, woolly rhinoceros
Plains (Temperate)
ankheg, aurochs, bison, cat, centaur, cockatrice, dire tiger, giant scorpion, goblin, gorgon, guardian naga, horse, pegasus, pony, worg
Plains (Warm)
ankheg, ankylosaurus, brachiosaurus, cat, cheetah, dire hyena, dire lion, dire tiger, elephant, giant frilled lizard, giant scorpion, gnoll, gold dragon, hyena, lion, monitor lizard, pegasus, rhinoceros, stegosaurus, triceratops, tyrannosaurus
Planar (Abaddon—Neutral Evil)
cauchemar, night hag, nightmare
Planar (Abyss—Chaotic Evil)
babau, balor, bebilith, dretch, glabrezu, hezrou, marilith, nabasu, nalfeshnee, quasit, retriever, shadow demon, succubus, vrock
Planar (Elysium—Chaotic Good)
astral deva, bralani, ghaele, lillend, planetar, solar
Planar (Heaven—Lawful Good)
astral deva, hound archon, lantern archon, planetar, solar, trumpet archon
Planar (Hell—Lawful Evil)
barbed devil, bearded devil, bone devil, erinyes, horned devil, ice devil, imp, lemure, pit fiend
Planar (Plane of Air)
air elemental, air mephit, djinni, dust mephit, ice mephit, invisible stalker
Planar (Plane of Earth)
earth elemental, earth mephit, salt mephit, shaitan, xorn
Planar (Plane of Fire)
efreeti, fire elemental, fire mephit, magma mephit, salamander, steam mephit
Planar (Plane of Water)
marid, ooze mephit, water elemental, water mephit
Swamp (Cold)
dire tiger, gray ooze, tarn linnorm, will-o'-wisp
Swamp (Temperate)
boggard, chuul, dire tiger, dracolisk, froghemoth, giant flytrap, giant frog, giant leech, giant slug, goblin dog, green hag, harpy, hydra, leech swarm, lizardfolk, medusa, ochre jelly, shambling mound, spirit naga, stirge, will-o'-wisp
Swamp (Warm)
black dragon, constrictor snake, crocodile, dire crocodile, dire tiger, giant frog, giant leech, giant slug, leech swarm, manticore, poison frog, shocker lizard, stirge, will-o'-wisp
Underground
basidirond, black pudding, cave fisher, centipede swarm, choker, cloaker, dark creeper, dark stalker, dark naga, darkmantle, derro, dracolisk, drider, drow, drow noble, duergar, gelatinous cube, giant centipede, giant slug, giant scorpion, gibbering mouther, goblin dog, gorgon, gray ooze, half-fiend minotaur, intellect devourer, kobold, medusa, mite, morlock, neothelid, ochre jelly, orc, otyugh, purple worm, roper, rust monster, shoggoth, skum, svirfneblin, troglodyte, vegepygmy, violet fungus, yellow musk creeper
Urban