| Name | CR | Type | Environment |
| Salamander | 6 | outsider (extraplanar, fire) | any warm (Plane of Fire) |
| Sapient Purple Orb, Luminant | 11 | aberration | any |
| Sapient Purple Orb | 4 | aberration | any |
| Sarcesian, Sarcesian Cybercommando | 8 | humanoid (sarcesian) | any low-gravity (Diaspora) |
| Sarcesian, Sarcesian Sniper | 5 | humanoid (sarcesian) | any low-gravity (Diaspora) |
| Sazaron, Sazaron Sage | 12 | monstrous humanoid | any (Arkanen) |
| Sazaron, Sazaron Scholar | 5 | monstrous humanoid | any (Arkanen) |
| Scavenger Slime | 9 | ooze | any |
| Sceaduinar | 7 | outsider (extraplanar) | any (Negative Energy Plane) |
| Scholars, Field Biologist | 7 | magical beast | — |
| Scholars, Postgrad Student | 1 | monstrous humanoid | — |
| Scholars, Scholar Of Magic | 11 | magical beast | — |
| Scholars, Subject Expert | 5 | magical beast | — |
| Scouring Swarm | 2 | aberration (swarm) | any |
| Scrap-bot | 1/2 | construct (technological) | any urban |
| Scrawler | 6 | animal (water) | aquatic (Weydana-5) |
| Scyphozoan | 3 | aberration | temperate aquatic or urban (Primoria) |
| Security Forces, Detective | 5 | humanoid (shirren) | — |
| Security Forces, Security Guard | 1 | humanoid (human) | — |
| Security Forces, Security Specialist | 3 | humanoid (android) | — |
| Seed Walker | 14 | plant | temperate and warm hills, forests, and plains |
| Selamid | 6 | ooze (selamid) | any (Silselrik) |
| Sentinel Tree | 7 | plant | any urban |
| Seprevoi | 3 | monstrous humanoid (seprevoi) | any (Sepres VI) |
| Shadow Hopper | 8 | magical beast (shapechanger) | any |
| Shadow Mastiff | 5 | outsider (evil, extraplanar) | any (Shadow Plane) |
| Shakalta, Shakalta Star-Guardian | 7 | humanoid (shakalta) | any (Accara IV) |
| Shantak | 8 | magical beast | cold mountains or vacuum |
| Sharpwing | 8 | animal | any cold (Aballon) |
| Shatori, Shatori Analyst | 4 | humanoid (shatori) | any (Perdure) |
| Shatori, Shatori Theorist | 10 | humanoid (shatori) | any (Perdure) |
| Shimreen | 5 | humanoid (shimreen) | any (Shimrinsara) |
| Shimreen, Shimreen Warrior | 5 | humanoid (shimreen) | any (Shimrinsara) |
| Shimreen, Shimreen Worker | 1 | humanoid (shimreen) | any (Shimrinsara) |
| Shipkiller Bulb | 18 | plant | any sky (gas giant) or vacuum |
| Shipmind | 13 | ooze | any (Dominion of the Black starships) |
| Shobhad | 4 | monstrous humanoid | cold deserts or mountains (Akiton) |
| Shobhad, Shobhad Warleader | 7 | monstrous humanoid | cold deserts or mountains (Akiton) |
| Shodrav | 11 | outsider (evil, extraplanar) | any (Shadow Plane) |
| Shotalashu, Feral Shotalashu | 6 | magical beast | warm forests (Castrovel) |
| Shotalashu | 2 | magical beast | warm forests (Castrovel) |
| Siktempora, Wanderlust | 11 | outsider (chaotic, extraplanar) | any (Dimension of Time) |
| Silicanid | 2 | animal (fire) | any land (Waydana-1) |
| Silicon Mummy, Mummified Prophet | 12 | undead | any |
| Sivv Sage-Coffer | 17 | construct (magical, sivv, technological) | any (Davvirex or Ark Prime) |
| Sivv Warmaster | 17 | aberration (sivv) | any (Davvirex or Ark Prime) |
| Skarak | 13 | magical beast | any land |
| Skathoil | 13 | Aberration | any |
| Skittermander | 2 | humanoid (skittermander) | any (Vesk-3) |
| Skittermander, Skittermander Whelp | 1/3 | humanoid (skittermander) | any (Vesk-3) |
| Skreeling | 3 | aberration | any hills or mountains |
| Skreesire | 7 | aberration | any hills or mountains |
| Skreesire, Skreeling | 3 | aberration | any hills or mountains |
| Skreesire | 7 | aberration | any hills or mountains |
| Skrell | 8 | aberration | any (Shadari Confederacy) |
| Sky Fisher | 5 | aberration | any sky (Castrovel) |
| Skysail | 5 | plant | any sky (Liavara) |
| Solar Wisp, Juvenile Solar Wisp | 5 | outsider (air, elemental, fire, native) | temperate or warm land or vacuum |
| Solar Wisp, Mature Solar Wisp | 19 | outsider (air, elemental, fire, native) | temperate or warm land or vacuum |
| Sombrian, Lumyr | 8 | fey | any |
| Sombrian, Solmyr | 13 | fey | any |
| Songtwisted | 5 | humanoid (shirren) | Vharrine |
| Spathinae, Spathinae Explorer | 11 | monstrous humanoid | any |
| Spathinae, Spathinae Guard | 1 | monstrous humanoid | any |
| Spectra, Aspecna | 18 | outsider (extraplanar, spectra) | any (the Drift) |
| Spectra, Excuba | 4 | outsider (extraplanar, spectra, swarm) | any (the Drift) |
| Spectra, Iridia | 8 | outsider (extraplanar, spectra) | any (the Drift) |
| Spectra, Nacrea | 16 | outsider (extraplanar, spectra) | any (the Drift) |
| Spectra, Sondria | 14 | outsider (extraplanar, spectra) | any (the Drift) |
| Spectra, Wyspiria | 11 | outsider (extraplanar, spectra) | any (the Drift) |
| Spewer | 10 | undead | any |
| Spookfish Swarm | 16 | undead (incorporeal, swarm) | warm land (Akiton) |
| Sports Figures, Battleflower Master | 16 | humanoid (ryphorian) | — |
| Sports Figures, Brutaris Lock-back | 10 | magical beast | — |
| Sports Figures, Magical Duelist | 6 | magical beast | — |
| Sports Figures, Parabolas Revivalist | 2 | humanoid (shimreen) | — |
| Squox | 1/3 | animal | any |
| Squox, Trained Squox | 1 | animal | any |
| Starmetal Eater, Abysium Eater | 5 | ooze | any |
| Starmetal Eater, Horacalcum Eater | 13 | ooze | any |
| Statikete | 15 | magical beast | any |
| Stelezorn | 7 | fey (shapechanger) | any urban |
| Stewards, Constable | 7 | humanoid (aquatic) | — |
| Stewards, Data Analyst | 5 | monstrous humanoid | — |
| Stewards, Ops Infiltrator | 15 | humanoid (ryphorian) | — |
| Stewards, Overwatch Captain | 10 | monstrous humanoid | — |
| Stomakera | 5 | magical beast | plains (Weydana-2) |
| Stormghost | 15 | monstrous humanoid | any |
| Stralithid | 8 | magical beast | any land (Weydana-7) |
| Street Gangs, Gang Machinist | 3 | humanoid (android) | — |
| Street Gangs, Gang Pusher | 2 | humanoid (ysoki) | — |
| Street Gangs, Gang Tough | 1/2 | humanoid (human) | — |
| Stridermander | 3 | monstrous humanoid (skittermander) | any (Vesk-3) |
| Stridermander, Stridermander Tyrant | 10 | monstrous humanoid (skittermander) | any (Vesk-3) |
| Stroxha | 8 | magical beast | temperate or warm forests (Marata) |
| Supenga, Pup | 5 | plant | warm or temperate deserts |
| Supenga, Titan | 15 | plant | warm and temperate deserts |
| Surnoch | 9 | animal | any underground or vacuum (Diaspora) |
| Survivalists, Career Ranger | 3 | humanoid (kobold) | — |
| Survivalists, Mysterious Hermit | 14 | aberration (shapechanger) | — |
| Survivalists, Off-gridder | 1/2 | humanoid (ryphorian) | — |
| Survivalists, Trophy Hunter | 9 | humanoid (pahtra) | — |
| Svartalfar | 9 | fey (extraplanar) | any (Shadow Plane) |
| Swamp Strider, Common | 2 | animal | any marsh (Castrovel) |
| Swamp Strider, Crested | 10 | animal | any marshes (Castrovel) |
| Symbiend, Damoritosh's Arm Host | 6 | humanoid (human) | any |
| Symbiend | 1/3 | aberration | any |
| Synapse Worm | 2 | vermin | any warm or temperate |
| Syngnathrix, Deep Mage Apprentice | 1/2 | Monstrous humanoid (aquatic) | — |