| Name | Level | Stat | Type |
|---|---|---|---|
| Only the Card Explodes First | - | ATK +8 | Event |
| Only ten dollars. | - | EVA +12 | Event |
| Only 1 gold. | - | DEF +2 | Event |
| Onigiri | 60 | ATK +8 | Enemy Kills |
| One-eyed | 58 | CRIT +4 | Enemy Kills |
| One-Horned Giant | 78 | DEF +4 | Enemy Kills |
| One-Handed | 80 | ATK +8 | Character Growth |
| One-Eyed | 48 | SPD +16 | Enemy Kills |
| One-Day Hero | - | Max HP +40 | Astral Adventures |
| One-Armed Hero | 100 | Max HP +40 | Astral Adventures |
| One shot, one kill. | 80 | ATK +8 | Character Growth |
| One on the left and one on the right. | 70 | SPD +16 | Conversations |
| One million. | - | Max HP +20 | Event |
| One Punch | 85 | EVA +16 | Enemy Kills |
| One Day Flower | - | - | Gathering |
| One Behind is on Fire 🔥 | - | ATK +24 | Event |
| Once in a thousand | - | - | Gathering |
| On the water. | 105 | CRIT +4 | Enemy Kills |
| On the ramp | - | ATK +4 | Event |
| On summer vacation. | - | DEF +8 | Event |
| On Fire | - | - | Senshi |
| On Christmas Eve | - | ATK +6 | Event |
| Omnivorous | 55 | Max HP +40 | Enemy Kills |
| Omniscient | 102 | Max HP +40 | Enemy Kills |
| Omniscient | 38 | - | Conversations |
| Omnipresent | - | - | Cooking |
| Old fart | 100 | EVA +16 | Enemy Kills |
| Old Shooter | 70 | Max HP +40 | Astral Adventures |
| Old River Lake | 100 | DEF +4 | Enemy Kills |
| Old Man | 75 | EVA +16 | Enemy Kills |
| Old Lady | 10 | - | Enemy Kills |
| Old God is here. | 10 | - | Other |
| Old | 93 | DEF +4 | Enemy Kills |
| Oh God, answer me. | - | DEF +8 | Event |
| Ogre | 85 | SPD +16 | Enemy Kills |
| Offline | 48 | SPD +16 | Enemy Kills |
| Officer | 30 | ATK +8 | Enemy Kills |
| Offering to heavens. | 100 | ATK +8 | Enemy Kills |
| Offensive-Minded | - | - | Crafting |
| Offending Taboos | - | - | Fishing |
| Off-Tune Master | - | - | Senshi |
| Off | 85 | EVA +16 | Enemy Kills |
| Odie | 90 | SPD +16 | Conversations |
| Oddball | 50 | Max HP +40 | Astral Adventures |
| Odd | 28 | Max HP +40 | Enemy Kills |
| Oda Nobunaga | - | - | Fishing |
| Ocean Overlord | - | - | Treasure Hunter |
| Ocean Lord | - | - | Other |
| Ocean Hunter | - | - | Fishing |
| Ocean Current | - | - | Treasure Hunter |