| Name | CR | Type | Environment |
| Yaruk | 8 | animal | temperate plains and forests (Castrovel) |
| Yithian | 9 | aberration | any |
| Yithian, Yithian Elder | 13 | aberration | any |
| Yotuhn | 11 | monstrous humanoid (giant) | any (Chonax) |
| Yrgytchee | 5 | monstrous humanoid | any (Yrgytch) |
| Yurei | 12 | undead | any |