Ogdoadic Serpent Strike
Ogdoadic Water Lily
Ogre of the Black Shadow
Ogre of the Scarlet Sorrow
Oh F!sh!
Oh my Trap Hole!
Oh Tokenbaum!
Ohime the Manifested Mikanko
Oil
Oilman
Oily Cicada
Ojama Black
Ojama Blue
Ojama Country
Ojama Delta Hurricane!!
Ojama Duo
Ojama Emperor
Ojama Green
Ojama King
Ojama Knight
Ojama Pajama
Ojama Pink
Ojama Red
Ojama Token
Ojama Trio
Ojama Yellow
Ojamagic
Ojamandala
Ojamassimilation
Ojamatch
Ojamuscle
Okiku's Dish Count
Old Entity Cthugua
Old Entity Hastorr
Old Mind
Old Vindictive Magician
Omega Goggles
Omega Judgment
Omega Summon
Ominous Fortunetelling
Omni Dragon Brotaur
On Your Mark, Get Set, DUEL!
Once Upon a Fairy Tail
One by One
One Day of Peace
One for One
One or Eight
One Who Hunts Souls
One-Eyed Shield Dragon
One-Eyed Skill Gainer
One-Kuri-Way
One-Shot Wand
One-Time Passcode
One-Way Synchro
Oneiros, the Dream Mirror Erlking
Oneiros, the Dream Mirror Tormentor
Oni Tank T-34
Oni-Gami Combo
Onibimaru Soul Sweeper
Onikuji