| Name | CR | Type | Environment |
| Baba Yaga's Rider, Black Rider | 13 | fey | any |
| Baba Yaga's Rider, Red Rider | 12 | fey | any |
| Baba Yaga's Rider, White Rider | 11 | fey | any |
| Baboon | 1/2 | animal | warm forests or plains |
| Bacallia | 1 | animal | temperate hills or mountains |
| Badger | 1/2 | animal
| temperate forests
|
| Badger, Dire Badger | 2 | animal
| temperate forests
|
| Baetriov | 8 | undead | any urban |
| Bagiennik | 6 | fey (aquatic) | cold rivers |
| Bagman | 4 | fey | any urban |
| Bakekujira | 17 | undead (aquatic) | any oceans |
| Baku | 8 | magical beast | any |
| Baku Dreamweaver | 11 | magical beast | any |
| Bandersnatch | 17 | magical beast | any forests |
| Banelight | 12 | fey | any |
| Banshee | 13 | undead (incorporeal)
| any
|
| Baregara | 12 | outsider (chaotic, evil, extraplanar) | warm forests (Abyss) |
| Barghest | 4 | outsider (evil, extraplanar, lawful, shapechanger) | any |
| Barghest, Greater Barghest | 7 | outsider (evil, extraplanar, lawful, shapechanger) | — |
| Barometz | 15 | plant | any forests |
| Barrow Hound | 6 | fey | any (the First World) |
| Basavan | 15 | monstrous humanoid | temperate forests or mountains |
| Basidirond | 5 | plant | any non-cold underground |
| Basilisk | 5 | magical beast | any |
| Bat, Bat Swarm | 2 | animal (swarm) | any temperate or tropical |
| Bat, Dire Bat | 2 | animal | any temperate or tropical |
| Bat, Mobat | 3 | magical beast
| temperate or warm forests, hills, or underground
|
| Bat, Skaveling | 5 | undead
| any underground
|
| Bat, Sootwing Bat | 1/2 | undead | any land |
| Baykok | 9 | undead | any |
| Bear, Dire Bear (Cave Bear) | 7 | animal | cold forests |
| Bear, Dire Polar Bear | 8 | animal | cold coastlines or plains |
| Bear, Grizzly Bear | 4 | animal | cold forests |
| Bear, Polar Bear | 5 | animal | cold coastlines or plains |
| Beatific One | 9 | outsider (asura, evil) | any |
| Bebilith | 10 | outsider (chaotic, evil, extraplanar) | any (the Abyss) |
| Bee, Giant Bee | 1 | vermin
| temperate or warm plains
|
| Bee, Giant Queen Bee | 5 | vermin
| temperate or warm plains
|
| Beetle, Dark Spitter Beetle | 3 | vermin | any underground |
| Beetle, Fire Beetle | 1/3 | vermin | any |
| Beetle, Giant Stag Beetle | 4 | vermin | temperate forests |
| Beetle, Goliath Stag Beetle | 8 | vermin
| warm forests or plains
|
| Beetle, Juggernaut Beetle | 14 | magical beast | any underground |
| Beetle, Scarab Beetle | 6 | vermin | warm deserts (Osirion) |
| Beetle, Slicer Beetle | 4 | vermin
| temperate forests
|
| Beetle, Stalk Beetle | 2 | vermin | warm deserts (Rahadoum) |
| Beheaded | 1/3 | undead | any |
| Beheaded, Flaming Skull | 1/2 | undead | any |
| Beheaded, Giant Beheaded | 2 | undead | any |
| Beheaded, Medusa Head | 3 | undead | any |
| Beheaded, Severed Head | 1/3 | undead | any |
| Beheaded, Skull Swarm | 1 | undead (swarm) | any |
| Behemoth, Ravener | 18 | magical beast | any forest, hill, jungle, or plains |
| Behemoth, Tempest Behemoth | 22 | magical beast (air, behemoth) | any air |
| Behemoth, Thalassic Behemoth | 20 | magical beast (aquatic, behemoth, water) | any water |
| Behemoth, Thunder Behemoth | 18 | magical beast (behemoth, earth) | any land |
| Behir | 8 | magical beast | warm hills and deserts |
| Belker | 6 | outsider (air, elemental, evil)
| any (Plane of Air)
|
| Belostomatid | 3 | vermin | temperate lakes, rivers, or swamps |
| Benaioh, Benaioh (Clay Vessel) | 7 | construct | any mountains or underground |
| Benaioh, Benaioh (Ooze Form) | 7 | ooze | any mountains or underground |
| Berbalang | 6 | undead | any land |
| Bhole | 17 | magical beast | any underground |
| Bhuta | 11 | undead (incorporeal) | any aboveground natural area |
| Biloko | 1/2 | fey | warm forests |
| Birelu | 10 | outsider (extraplanar, incorporeal) | any forest, mountain, or plains |
| Bisha Ga Tsuku | 9 | outsider (cold, native) | cold hills or mountains |
| Black Jinni | 12 | outsider (chaotic, evil, extraplanar) | warm deserts |
| Black Pudding | 7 | ooze | any underground |
| Black Shuck | 7 | magical beast | temperate coasts or marshes |
| Blackwisp Egret | 1/3 | animal | temperate swamps |
| Blast Shadow | 5 | undead (fire) | — |
| Blight, Cave Blight | 19 | ooze (blight) | any underground |
| Blight, Desert Blight | 13 | ooze (blight) | any deserts |
| Blight, Forest Blight | 18 | ooze (blight) | any forests |
| Blight, Mountain Blight | 14 | ooze (blight) | any mountains |
| Blight, Sewer Blight | 15 | ooze (blight) | any underground (sewers) |
| Blight, Swamp Blight | 17 | ooze (aquatic, blight) | any swamps |
| Blight, Tundra Blight | 16 | ooze (blight, cold) | cold plains or glaciers |
| Blighted Fey (Satyr) | 6 | fey | temperate forests (Nirmathas) |
| Blighted Fey Satyr | 6 | fey | temperate forests |
| Blightspawn | 5 | aberration | any swamps |
| Blightspawn of Ghlaunder | 5 | aberration | — |
| Blindheim | 2 | magical beast
| any underground
|
| Blink Dog | 2 | magical beast
| temperate plains or forests
|
| Blodeuwedd | 6 | fey | temperate plains |
| Blood Algae Swarm | 8 | plant (swarm) | temperate or warm rivers |
| Blood Bramble | 10 | plant | temperate forests |
| Blood Lily | 10 | plant (aquatic) | warm coastlines or underwater |
| Blood Maize | 2 | plant | temperate or warm plains |
| Blood Queen | 23 | outsider (native) | any |
| Bloodbrush | 2 | plant | cold or temperate plains |
| Bloodhaze Mosquito Swarm | 6 | vermin (swarm) | warm forests and swamps |
| Bloodless Vessel | 12 | undead | — |
| Bloodplate Burster | 9 | plant | temperate or warm deserts or plains |
| Bloody Bones | 10 | undead | any land |
| Boar | 2 | animal | temperate or tropical forests |
| Boar, Bristle Boar | 3 | animal | any plains or hills |
| Boar, Dire Boar (Daeodon) | 4 | animal | temperate or tropical forests |
| Bodak | 8 | undead (extraplanar)
| any land (evil Outer Plane)
|
| Bodythief | 14 | plant | temperate or warm forests |
| Bodythief, Pod-Spawned Guard Captain | 8 | plant (augmented humanoid) | any |
| Bog Strider | 2 | monstrous humanoid | temperate or warm swamps |
| Bogeyman | 10 | fey | any |
| Boggard | 2 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Abyssal Warrior | 8 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Brute | 3 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Champion | 7 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Farcroaker | 3 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Hunter | 5 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Priest-King | 11 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Prophet | 5 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Savage | 4 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Scarred One | 6 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Stalker | 9 | humanoid (boggard) | temperate marshes |
| Boggard, Boggard Swampseer | 4 | humanoid (boggard) | temperate marshes |
| Boggart | 4 | fey | temperate
forests or swamps |
| Boggle | 8 | fey (shapechanger) | any land |
| Bogwid | 5 | aberration | any swamps or underground |
| Bogwiggle | 1 | aberration (aquatic) | temperate swamps |
| Boilborn | 1 | ooze | any |
| Bolla | 14 | magical beast | cold or temperate mountains |
| Bone Priest | 4 | undead | any |
| Bone Ship | 18 | undead (water) | any oceans |
| Bonestorm | 8 | undead (swarm) | any |
| Bonethorn | 12 | plant | any |
| Bonewrought Willow | 3 | plant (extraplanar) | any land (The Boneyard) |
| Bore Worm, Bore Worm Monarch | 7 | vermin | any underground |
| Bore Worm, Bore Worm Swarm | 5 | vermin (swarm) | any underground |
| Bore Worm, Empress Bore Worm | 10 | vermin | any underground |
| Boreal Creature, Boreal Annis Hag | 7 | monstrous humanoid (cold) | cold marshes |
| Boreal Creature, Boreal Manticore | 6 | magical beast (cold) | cold forests |
| Boreal Creature, Boreal Wolf | 2 | magical beast (cold) | cold forests |
| Boruta | 9 | plant | any |
| Botfly, Botfly Swarm | 4 | vermin (swarm) | warm jungles and swamps |
| Botfly, Giant Botfly | 1/3 | vermin | warm jungle |
| Brain Mole | 1 | magical beast | temperate forests, hills, or plains |
| Brain Mole, Brain Mole Monarch | 5 | magical beast | temperate forests, hills, or plains |
| Brain Ooze | 7 | ooze | any ruins or underground |
| Bramble Throne | 16 | plant | temperate forests |
| Brambleblight | 7 | plant | temperate or warm forests or underground |
| Bramblelash | 1 | plant | cold or temperate forests |
| Breathless Orchid | 2 | plant | temperate forests |
| Brethedan | 5 | aberration | any sky |
| Broken Soul, Broken Soul Lillend | 9 | outsider (azata, chaotic, extraplanar, evil) | any |
| Brownie | 1 | fey
| temperate forests or plains
|
| Bugbear | 2 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Ambusher | 10 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Bloodmage | 11 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Cultist | 7 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Flesh Glutton | 8 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Gnasher | 4 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Lurker | 8 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Shadow Sneak | 10 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Stalker | 5 | humanoid (goblinoid) | temperate mountains |
| Bugbear, Bugbear Tyrant | 13 | humanoid (goblinoid) | temperate mountains |
| Buggane | 5 | monstrous humanoid | any underground |
| Bulabar | 1 | fey | any (First World) |
| Bulette | 7 | magical beast | temperate hills |
| Bulette, Xenarth | 10 | outsider (chaotic, demon, evil, native) | — |
| Bunyip | 3 | magical beast (aquatic)
| any aquatic
|
| Buraq | 5 | magical beast | warm mountains |
| Burleev | 4 | outsider (cold or fire, extraplanar) | any (Maelstrom) |
| Burning Child | 10 | undead (fire) | temperate plains |
| Burstigeit | 3 | magical beast | any underground |
| Byakhee | 4 | aberration | any air |