| Name | CR | Type | Environment |
| Ignurso, Burrower | 5 | magical beast | warm mountains and underground |
| Ignurso, Mason | 11 | magical beast | warm and temperate mountains and underground |
| Ihonva | 4 | monstrous humanoid | warm desert (Verces) |
| Ijtikri | 1/2 | aberration | any (Vesk-2) |
| Ijtikri, Ijtikri Commando | 4 | aberration | any (Vesk-2) |
| Ikeshti, Ikeshti Brood-Minder | 2 | humanoid (ikeshti) | any deserts, hills, or mountains (Akiton) |
| Ikeshti, Ikeshti Rivener | 5 | humanoid (ikeshti) | any deserts, hills, or mountains (Akiton) |
| Ilthisarian | 4 | monstrous humanoid (ilthisarian) | any swamp (Arshalin) |
| Immolsivix | 13 | magical beast | any jungle or underground (Kehtaria) |
| Impostor | 8 | outsider (extraplanar) | any (Astral Plane) |
| Inevitable, Anhamut | 10 | outsider (inevitable, lawful) | any |
| Infiltration Robot, Exterminator-class | 7 | construct (technological) | Any |
| Infiltration Robot, Monitor-class | 2 | construct (technological) | Any |
| Infiltrators, Double Agent | 8 | humanoid (kobold) | — |
| Infiltrators, Hacker | 5 | construct (technological) | — |
| Infiltrators, Shapeshifter | 11 | aberration (shapechanger) | — |
| Infiltrators, Spy | 14 | aberration | — |
| Investigators, Conspiracist | 1 | monstrous humanoid | — |
| Investigators, Detective | 7 | monstrous humanoid | — |
| Investigators, Paranormal Investigator | 10 | humanoid (hadrogaan) | — |
| Investigators, Psychic Seer | 4 | magical beast | — |
| Irokiroi | 5 | animal | any sky (Osoro) |
| Irokiroi, Oshirokiroi | 12 | animal | any sky (Osoro) |
| Itmi Vruh | 5 | undead (incorporeal) | any |
| Itmi Vruh, Reminiscent | 10 | undead (incorporeal) | any |
| Ixtangi, Disruptor | 7 | monstrous humanoid | any |
| Ixtangi | 1 | monstrous humanoid | any |
| Izalguun, Izalguun Healer | 8 | monstrous humanoid | any (Izalraan) |
| Izalguun, Izalguun Hunter | 4 | monstrous humanoid | any (Izalraan) |
| Iztheptar | 6 | humanoid | any |