| Name | CR | Type | Environment |
| Rabisu | 11 | fey | warm deserts, hills, and mountains |
| Radiant Essence | 13 | ooze | any land |
| Ragewight | 6 | undead | temperate hills (necropolis of Nogortha) |
| Raiju | 5 | outsider (air, extraplanar, shapechanger) | any land or sky (lightning storms) |
| Rajbut Ambari | 7 | undead | warm forests |
| Rakshasa | 10 | outsider (native, shapechanger) | any |
| Rakshasa, Amanusya | 6 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Avatarana | 12 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Dandasuka | 5 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Marai | 8 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Orsatka | 13 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Rakshasa Maharaja | 20 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Raktavarna | 2 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Tataka | 15 | outsider (native, rakshasa, shapechanger) | any |
| Rakshasa, Zalyakavat | 13 | outsider (native, rakshasa, shapechanger) | any |
| Ramidreju | 1/2 | magical beast | any land |
| Rast | 5 | outsider (extraplanar, fire) | any (Plane of Fire) |
| Rat King | 5 | magical beast | any urban or underground |
| Rat, Dire Rat | 1/3 | animal | any urban |
| Rat, Rat Swarm | 2 | animal (swarm) | any |
| Ratfolk | 1/3 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Bravo | 2 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Caravan Guard | 3 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Chemist | 7 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Elder | 8 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Expedition Leader | 7 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Sage | 6 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Tinkerer | 1 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Troubleshooter | 5 | humanoid (ratfolk) | warm deserts or urban |
| Ratfolk, Ratfolk Warden | 4 | humanoid (ratfolk) | warm deserts or urban |
| Ratling | 2 | magical beast | any urban |
| Raven Swarm | 3 | animal (swarm) | any temperate |
| Ravener, Red Wyrm Ravener | 22 | undead (fire) | warm mountains |
| Rawhead | 14 | monstrous humanoid | any land |
| Ray, Manta Ray | 1 | animal (aquatic) | warm oceans |
| Ray, Stingray | 1/2 | animal (aquatic) | warm oceans |
| Razormouth | 11 | vermin | temperate mountains |
| Reaper, Grim Reaper | 20 | undead (evil, extraplanar, incorporeal) | any |
| Reaper, Minor Reaper | 10 | undead (evil, extraplanar) | any |
| Recycled Gearsman | 3 | construct (robot) | any |
| Red Reaver | 13 | magical beast | temperate hills |
| Redcap | 6 | fey | temperate forests, mountains, or underground |
| Redkind | 2 | fey | any urban |
| Reefclaw | 1 | aberration (aquatic) | any water (coastal) |
| Remacera | 6 | fey | any forests and hills (First World) |
| Remorhaz | 7 | magical beast | cold deserts and glaciers |
| Reptoid | 1/2 | humanoid (reptilian, shapechanger) | any land |
| Retriever | 11 | construct (extraplanar) | any (Abyss) |
| Revenant | 6 | undead | any land |
| Rhinoceros | 4 | animal | warm plains |
| Rhinoceros, Woolly Rhinoceros | 6 | animal | cold plains |
| Rhu-chalik | 6 | aberration | any |
| Riftcreeper | 15 | ooze (extraplanar) | any mountains (Abyss) |
| Ringhorn | 1 | animal | temperate hills and plains |
| Robot, Annihilator Robot | 16 | construct (robot) | any |
| Robot, Arachnid Robot | 1/2 | construct (robot) | any (Numeria) |
| Robot, Collector Robot | 3 | construct (robot) | any (Numeria) |
| Robot, Director Robot | 10 | construct (robot) | any (Numeria) |
| Robot, Evaluator Robot | 12 | construct (robot) | any (Numeria) |
| Robot, Gearsman Robot | 4 | construct (robot) | any |
| Robot, Gladiator Robot | 17 | construct (robot) | any |
| Robot, Juggernaut Robot | 15 | construct (robot) | any (Numeria) |
| Robot, Mannequin Robot | 2 | construct (robot) | any (Numeria) |
| Robot, Myrmidon Robot | 11 | construct (robot) | any |
| Robot, Observer Robot | 2 | construct (robot) | any (Numeria) |
| Robot, Observer Robot Swarm | 10 | construct (robot, swarm) | any (Numeria) |
| Robot, Octopod Mechanic Drone | 13 | construct (robot) | any |
| Robot, Reclamation Robot | 12 | construct (robot) | any |
| Robot, Repair Robot | 2 | construct (robot) | any |
| Robot, Scrapyard Robot | 3 | construct (robot) | any ruin (Numeria) |
| Robot, Surgeon Robot | 14 | construct (robot) | any (Numeria) |
| Robot, Terraformer Robot | 7 | construct (robot) | any |
| Robot, Thought Harvester Robot | 10 | construct (robot) | any (Numeria) |
| Robot, Torturer Robot | 8 | construct (robot) | any (Numeria) |
| Robot, Warden Robot | 9 | construct (robot) | any (Numeria) |
| Roc | 9 | animal | warm mountains |
| Rock Tuatara | 1/3 | animal | any underground |
| Roiling Oil | 6 | ooze | any underground |
| Rokurokubi | 14 | monstrous humanoid | any ruins |
| Roofgarden | 7 | plant | temperate forest or urban |
| Rope Dragon | 5 | dragon (shapechanger) | any urban |
| Roper | 12 | aberration | any underground |
| Rorkoun | 6 | aberration (aquatic) | temperate marshes and underground |
| Roseblood Sprite | 3 | fey | any forest |
| Roseling | 7 | plant (extraplanar, shapechanger) | any (Nirvana) |
| Rot Grub, Giant Rot Grub | 3 | vermin | any |
| Rot Grub, Rot Grub Swarm | 7 | vermin (swarm) | any |
| Rougarou | 1/2 | humanoid (shapechanger) | any land |
| Rukh | 10 | magical beast | warm deserts or mountains |
| Rukh, Juvenile Rukh | 3 | magical beast | warm mountains or deserts |
| Rune Guardian | 1 | construct | any (Thassilonian runes) |
| Runeslave, Runeslave Hill Giant | 8 | humanoid (giant)
| any
|
| Runewarped Gobline | 5 | aberration (augmented humanoid) | any |
| Rusalka | 12 | fey (aquatic) | any water |
| Rust Monster | 3 | aberration | any underground |
| Rust-Risen | 2 | undead | any |