| Name | Attribute | Level | Type |
|---|---|---|---|
| One-Horned Giant | 81 | General Monster | |
| 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 | 19 | Elite Monster | |
| Opaltoad | 49 | 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 | |
| Orcish Sprite | 55 | General Monster | |
| Ordinary Stone Statue | - | 1 | Interactive |
| Ore Mud Monster | 85 | General Monster | |
| Ore Pile | - | 90 | Interactive |
| Orid's Caravan Meyer | - | 1 | General |
| Osprae | - | 135 | Elite Monster |
| Osprae | - | 87 | Elite Monster |
| Osprae | - | 15 | Elite Monster |
| Osprae | - | 14 | Elite Monster |
| Osprae | - | 16 | Elite Monster |
| Osprae | - | 17 | Elite Monster |
| Osprae | - | 88 | Elite Monster |
| Osprae | - | 13 | Elite Monster |
| Osprae | - | 12 | Elite Monster |
| Osprae | - | 11 | Elite Monster |
| Osprae | - | 18 | Elite Monster |
| Osprae | - | 52 | Elite Monster |
| Osprae | - | 53 | Elite Monster |
| Osprae | - | 89 | Elite Monster |
| Osprae | - | 19 | Elite Monster |
| Osprae | - | 20 | Elite Monster |
| Osprae | - | 90 | Elite Monster |
| Osprae | - | 91 | Elite Monster |
| Osprae | - | 92 | Elite Monster |
| Osprae | - | 93 | Elite Monster |
| Osprae | - | 94 | Elite Monster |
| Osprae | - | 95 | Elite Monster |
| Osprae | - | 96 | Elite Monster |
| Osprae | - | 97 | Elite Monster |
| Osprae | - | 98 | Elite Monster |
| Osprae | - | 99 | Elite Monster |
| Osprae | - | 100 | Elite Monster |