| Ondu Champion | BFZ-149 |
| Ondu Giant | PCA-71 |
| Ondu Greathorn | BFZ-40 |
| Ondu Inversion // Ondu Skyruins | ZNR-30 |
| Ondu War Cleric | OGW-31 |
| One with Nature | SCG-125 |
| One with Nothing | SOK-84 |
| Oneirophage | MH1-60 |
| Onslaught | EXO-92 |
| Opal Lake Gatekeepers | DGM-16 |
| Ophidian | WTH-45 |
| Ophidian Eye | TSP-70 |
| Opportunity | ULG-37 |
| Opportunity | C17-89 |
| Oppression | USG-143 |
| Opt | DOM-60 |
| Opulent Palace | KTK-238 |
| Opulent Palace | OTC-307 |
| Oracle of Nectars | SHM-233 |
| Oran-Rief Invoker | DDR-17 |
| Orc Sureshot | FRF-78 |
| Orcish Artillery | 10E-220 |
| Orcish Cannonade | DDN-28 |
| Orcish Lumberjack | DDL-44 |
| Orcish Oriflamme | EMA-140 |
| Orcish Settlers | WTH-112 |
| Order of Midnight // Alter Fate | ELD-99 |
| Order of Yawgmoth | DDE-11 |
| Order of Yawgmoth | USG-144 |
| Oreskos Explorer | C21-98 |
| Oreskos Swiftclaw | M15-22 |
| Orim's Chant | PLS-11 |
| Ormos, Archive Keeper | JMP-13 |
| Ornithopter | M15-223 |
| Ornithopter of Paradise | MH2-232 |
| Orochi Eggwatcher // Shidako, Broodmistress | CHK-233 |
| Orvar, the All-Form | KHM-305 |
| Orzhov Advokist | C16-3 |
| Orzhov Basilica | C17-268 |
| Orzhov Enforcer | RNA-79 |
| Orzhov Guildgate | RNA-253 |
| Orzhova, the Church of Deals | GPT-162 |
| Ossification | ONE-26 |
| Otherworldly Journey | DDC-16 |
| Oubliette | 2XM-100 |
| Oust | DDP-7 |
| Outlaws' Merriment | ELD-198 |
| Outmaneuver | USG-205 |
| Outmuscle | ELD-170 |
| Outnumber | BFZ-150 |