SRD & OGL creatures — full stat blocks. Each entry links its source.
| Name | Type | Size | CR | Source |
|---|---|---|---|---|
| One-Headed Clockwork Dragon | Construct | Large | 8 | Creature Codex |
| One-Horned Ogre | Giant | Large | 5 | Tome of Beasts 2 |
| Oni | Giant | large | 7 | Black Flag SRD |
| Oni | Giant | Large | 7 | 5e Core Rules |
| Ophanim | Celestial | Large | 16 | Creature Codex |
| Ophidiotaur | Monstrosity | Large | 5 | Tome of Beasts 2 |
| Ophinix | Monstrosity | Large | 2 | Tome of Beasts 2 |
| Ophio Fungus | Plant | Huge | 7 | Tome of Beasts 2 |
| Orc | Humanoid | medium | 1/2 | Black Flag SRD |
| Orc | Humanoid | Medium | 1/2 | 5e Core Rules |
| Orc Warlord | Humanoid | medium | 4 | Black Flag SRD |
| Orcish Wildling Minstrel | Humanoid | Medium | 2 | Level Up Advanced 5e Monstrous Menagerie |
| Ork Urk | Humanoid | Medium | 2 | Level Up Advanced 5e Monstrous Menagerie |
| Orniraptor | Monstrosity | Small | 1/4 | Tome of Beasts 2 |
| Orobas Devil | Fiend | Large | 14 | Tome of Beasts |
| Orobas Devil | Fiend | Large | 14 | Tome of Beasts 2023 |
| Orphan of the Black | Fey | Small | 2 | Tome of Beasts 2 |
| Orthrus | Monstrosity | Medium | 3 | Creature Codex |
| Ortifex | Undead | Medium | 4 | Tome of Beasts 2 |
| Ostinato | Aberration | Medium | 4 | Tome of Beasts 2023 |
| Ostinato | Aberration | Medium | 4 | Tome of Beasts |
| Oth | Aberration | Large | 5 | Creature Codex |
| Otterfolk | Humanoid | Small | 1/4 | Tome of Beasts 2 |
| Otyugh | Aberration | Large | 5 | 5e Core Rules |
| Otyugh | Aberration | Large | 6 | Level Up Advanced 5e Monstrous Menagerie |
| Otyugh | Aberration | large | 5 | Black Flag SRD |
| Ouroban | Humanoid | Medium | 11 | Creature Codex |
| Ouroboros | Dragon | Huge | 6 | Creature Codex |
| Overshadow | Undead | Large | 4 | Tome of Beasts 2 |
| Owl Harpy | Monstrosity | Medium | 5 | Tome of Beasts |
| Owl Harpy | monstrosity | Medium | 5 | Tome of Beasts 2023 |
| Owlbear | Monstrosity | Large | 3 | 5e Core Rules |
| Owlbear | Monstrosity | Large | 3 | Level Up Advanced 5e Monstrous Menagerie |
| Construct |
| Large |
| 8 |
| Tome of Beasts 2 |
| Ooze |
| Gargantuan |
| 9 |
| Tome of Beasts |
| Ooze |
| Gargantuan |
| 9 |
| Tome of Beasts 2023 |
| Ooze |
| Large |
| 4 |
| Tome of Beasts 3 |
| Ooze |
| Medium |
| 1 |
| Tome of Beasts 3 |
| Ooze |
| Large |
| 12 |
| Tome of Beasts 3 |
| Ooze |
| Gargantuan |
| 10 |
| Tome of Beasts 3 |
| Ooze |
| Gargantuan |
| 4 |
| Tome of Beasts 3 |
| Ooze |
| Medium |
| 9 |
| Tome of Beasts 3 |
| Ooze |
| Huge |
| 7 |
| Tome of Beasts 3 |
| Beast |
| huge |
| 3 |
| Black Flag SRD |
| Beast |
| Tiny |
| 0 |
| 5e Core Rules |
| Beast |
| Tiny |
| 0 |
| Level Up Advanced 5e Monstrous Menagerie |
| Beast |
| tiny |
| 0 |
| Black Flag SRD |
| Beast |
| large |
| 1/4 |
| Black Flag SRD |