| Name | Attribute | Level | Type |
|---|---|---|---|
| One-Horned Giant | - | 1 | General |
| 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 |
| 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 | - | 121 | Elite Monster |
| Osprae | - | 120 | Elite Monster |
| Osprae | - | 122 | Elite Monster |
| Osprae | - | 119 | Elite Monster |
| Osprae | - | 123 | Elite Monster |
| Osprae | - | 124 | Elite Monster |
| Osprae | - | 125 | Elite Monster |
| Osprae | - | 118 | Elite Monster |
| Osprae | - | 117 | Elite Monster |
| Osprae | - | 116 | Elite Monster |
| Osprae | - | 126 | Elite Monster |
| Osprae | - | 115 | Elite Monster |
| Osprae | - | 127 | Elite Monster |
| Osprae | - | 114 | Elite Monster |
| Osprae | - | 128 | Elite Monster |
| Osprae | - | 129 | Elite Monster |
| Osprae | - | 113 | Elite Monster |
| Osprae | - | 130 | Elite Monster |
| Osprae | - | 131 | Elite Monster |
| Osprae | - | 112 | Elite Monster |
| Osprae | - | 132 | Elite Monster |
| Osprae | - | 133 | Elite Monster |
| Osprae | - | 134 | Elite Monster |
| Osprae | - | 135 | Elite Monster |
| Osprae | - | 111 | Elite Monster |
| Osprae | - | 110 | Elite Monster |
| Osprae | - | 136 | Elite Monster |