| Name | Attribute | Level | Type |
|---|---|---|---|
| Old Man | - | 1 | General |
| Old Man | - | 1 | General |
| Old Man Barley | - | 1 | General |
| Omu | - | 1 | General |
| On/Off | - | 1 | Interactive |
| Onami | - | 1 | General |
| Onami | - | 1 | General |
| One-Horned Giant | 81 | General Monster | |
| One-Horned Giant | 81 | General Monster | |
| One-Horned Giant | - | 1 | General |
| One-Horned Giant | - | 1 | General |
| One-Man Army Dominius | 31 | Boss Monster | |
| Onyx Axe Bazoros | 80 | World Boss | |
| Onyx Axe Bazoros | 80 | World Boss | |
| Opaltoad | 49 | Elite Monster | |
| Opaltoad | 19 | Elite Monster | |
| Opaltoad | 49 | Elite Monster | |
| Opaltoad | - | 19 | Elite Monster |
| Oran Grass | - | 1 | Interactive |
| Orc Rogue | 3 | General Monster | |
| Orcan Champion Skarr | 57 | General | |
| Orcan Champion Skarr | 57 | Boss Monster | |
| Orcan Chieftain Shazu | 55 | Boss Monster | |
| Orcan Guard | 53 | Elite Monster | |
| Orcan Guard Captain | 52 | Elite Monster | |
| Orchid | - | 1 | General |
| Orcish Sprite | 55 | General Monster | |
| Orcish Sprite | 55 | General | |
| Ordinary Stone Statue | - | 1 | Interactive |
| Ore Mud Monster | 85 | General Monster | |
| Ore Pile | - | 90 | Interactive |
| Orid's Caravan Meyer | - | 1 | General |
| Osprae | - | 82 | Elite Monster |
| Osprae | - | 24 | Elite Monster |
| Osprae | - | 14 | Elite Monster |
| Osprae | - | 13 | Elite Monster |
| Osprae | - | 9 | Elite Monster |
| Osprae | - | 12 | Elite Monster |
| Osprae | - | 11 | Elite Monster |
| Osprae | - | 7 | Elite Monster |
| Osprae | - | 50 | Elite Monster |
| Osprae | - | 51 | Elite Monster |
| Osprae | - | 10 | Elite Monster |
| Osprae | - | 52 | Elite Monster |
| Osprae | - | 53 | Elite Monster |
| Osprae | - | 143 | Elite Monster |
| Osprae | - | 6 | Elite Monster |
| Osprae | - | 144 | Elite Monster |
| Osprae | - | 5 | Elite Monster |
| Osprae | - | 139 | Elite Monster |