| Name | CR | MR | Type | Environment |
| Aboleth | 9 | 3 | aberration (aquatic, mythic) | any aquatic |
| Anunnaki | 18 | 7 | monstrous humanoid (mythic, shapechanger) | any |
| Apkallu | 23 | 9 | outsider (extraplanar, lawful, mythic, water) | any (lawful planes) |
| Apocalypse Locust | 6 | 3 | outsider (evil, extraplanar, mythic) | any evil-aligned planes |
| Argus | 13 | 6 | aberration (mythic) | any land |