| Ogdoadic OriginAncient Guardians · 011 | Ancient Guardians | 011 | Rare | €0.16 |
| Ogdoadic Serpent StrikeBattle of Chaos · 058 | Battle of Chaos | 058 | Common | €0.10 |
| Ogdoadic Water LilyAncient Guardians · 010 | Ancient Guardians | 010 | Super Rare | €0.10 |
| Ogre of the Black ShadowStarter Deck: Kaiba · 019 | Starter Deck: Kaiba | 019 | Common | €0.13 |
| Ogre of the Scarlet SorrowAbsolute Powerforce · 005 | Absolute Powerforce | 005 | Super Rare | $0.33 |
| Oh F!sh!Generation Force · 069 | Generation Force | 069 | Rare | $0.07 |
| Ohime the Manifested MikankoAmazing Defenders · 027 | Amazing Defenders | 027 | Ultra Rare | €3.44 |
| Oh Tokenbaum!Shadow Specters · 098 | Shadow Specters | 098 | Rare | €0.10 |
| OilBattles of Legend: Terminal Revenge · 026 | Battles of Legend: Terminal Revenge | 026 | Secret Rare | €1.70 |
| OilmanAbsolute Powerforce · 036 | Absolute Powerforce | 036 | Common | €0.06 |
| Oily CicadaBattles of Legend: Crystal Revenge · 027 | Battles of Legend: Crystal Revenge | 027 | Ultra Rare | €0.08 |
| Ojama BlackInvasion of Chaos · 002 | Invasion of Chaos | 002 | Common | €0.03 |
| Ojama BlueRaging Battle · 097 | Raging Battle | 097 | Rare | €0.36 |
| Ojama CountryRaging Battle · 098 | Raging Battle | 098 | Rare | €0.14 |
| Ojama Delta Hurricane!!Invasion of Chaos · 034 | Invasion of Chaos | 034 | Short Print | €0.05 |
| Ojama DuoCircuit Break · 080 | Circuit Break | 080 | Short Print | €0.59 |
| Ojama EmperorDuel Overload · 033 | Duel Overload | 033 | Ultra Rare | €0.23 |
| OjamagicElemental Energy · 040 | Elemental Energy | 040 | Common | €0.08 |
| Ojama GreenDark Crisis · 056 | Dark Crisis | 056 | Common | €0.12 |
| Ojama KingSoul of the Duelist · 034 | Soul of the Duelist | 034 | Rare | $0.29 |
| Ojama KnightTactical Evolution · 044 | Tactical Evolution | 044 | Common | €0.24 |
| OjamandalaUnlisted Printings | Unlisted Printings | — | — | — |
| Ojama PajamaLegendary Duelists: Ancient Millennium · 024 | Legendary Duelists: Ancient Millennium | 024 | Rare | €0.40 |
| Ojama PinkBlazing Vortex · 036 | Blazing Vortex | 036 | Common | €0.09 |
| Ojama RedRaging Battle · 096 | Raging Battle | 096 | Rare | €0.19 |
| OjamassimilationLegendary Duelists: Ancient Millennium · 022 | Legendary Duelists: Ancient Millennium | 022 | Rare | €0.28 |
| OjamatchLegendary Duelists: Ancient Millennium · 023 | Legendary Duelists: Ancient Millennium | 023 | Rare | €0.13 |
| Ojama TokenUnlisted Printings | Unlisted Printings | — | — | $21.39 |
| Ojama TrioDark Crisis · 047 | Dark Crisis | 047 | Short Print | $0.47 |
| Ojama YellowInvasion of Chaos · 001 | Invasion of Chaos | 001 | Common | €0.04 |
| OjamuscleElemental Energy · 041 | Elemental Energy | 041 | Common | €0.02 |
| Okiku's Dish CountDoom of Dimensions · 080 | Doom of Dimensions | 080 | Common | $0.07 |
| Old Entity CthuguaShadows in Valhalla · 016 | Shadows in Valhalla | 016 | Secret Rare | $0.57 |
| Old Entity Hastorr2015 Mega-Tins · 005 | 2015 Mega-Tins | 005 | Super Rare | €0.69 |
| Old MindChaos Impact · 066 | Chaos Impact | 066 | Common | $0.10 |
| Old Vindictive MagicianMagician's Force · 067 | Magician's Force | 067 | Common | €0.10 |
| Omega GogglesCrossroads of Chaos · 062 | Crossroads of Chaos | 062 | Short Print | $0.13 |
| Omega JudgmentDimension Force · 084 | Dimension Force | 084 | Common | €0.02 |
| Omega SummonFusion Enforcers · 037 | Fusion Enforcers | 037 | Secret Rare | €0.15 |
| Omega Vidolium the Power Patron of Heaven's EndUnlisted Printings | Unlisted Printings | — | — | — |
| Ominous FortunetellingLegacy of Darkness · 094 | Legacy of Darkness | 094 | Common | $0.18 |
| Omni Dragon BrotaurDark Neostorm · 020 | Dark Neostorm | 020 | Secret Rare | $0.13 |
| Once Upon a Fairy TailBlazing Dominion · 062 | Blazing Dominion | 062 | Common | €0.11 |
| One by OneLightning Overdrive · 078 | Lightning Overdrive | 078 | Common | €0.07 |
| One Day of PeacePhoton Shockwave · 060 | Photon Shockwave | 060 | Common | $1.22 |
| One-Eyed Shield DragonLegend of Blue Eyes White Dragon · 087 | Legend of Blue Eyes White Dragon | 087 | Common | €0.02 |
| One-Eyed Skill GainerAbyss Rising · 040 | Abyss Rising | 040 | Super Rare | $0.31 |
| One for OneRaging Battle · 045 | Raging Battle | 045 | Rare | $0.15 |
| Oneiros, the Dream Mirror ErlkingChaos Impact · 087 | Chaos Impact | 087 | Super Rare | €0.18 |
| Oneiros, the Dream Mirror TormentorBlazing Vortex · 042 | Blazing Vortex | 042 | Super Rare | €0.15 |