Obnoxious Celtic Guard
(Continuous) Obnoxious Resistance
Monsters you control whose ATK is lower than or equal to 1400 cannot be destroyed by battle when they battle with monsters whose ATK is greater than or equal to 1900. (Damage calculation is applied normally.)
Ocean Dragon Lord – Neo-Daedalus
(Ignition) Raging Tidal Splash
Send 1 "Umi" in your hand or that you control to the Graveyard. Send up to 3 cards on the field and/or randomly from your opponent's hand to the Graveyard. This Ability can only be used during your Main Phase.
(Continuous) Water Default
While there is no face-up Field Spell Card on the field, this Ability is active. You are considered to control "Umi". All Fish, Sea Serpent, Thunder and Aqua-Type monsters on the field gain 200 ATK and DEF. All Machine and Pyro-Type monsters on the field lose 200 ATK and DEF.
Ocean's Keeper
(Continuous) Umi Stronghold
While you control "Umi", this Ability is active. "Umi" cannot be destroyed by a card effect. All Fish, Sea Serpent, Thunder and Aqua-Type monsters on the field gain 200 ATK and DEF. All Machine and Pyro-Type monsters on the field lose 200 ATK and DEF.
Ojama King
(Ignition) Ojama Reinforcement
Pay 500 Life Points. Special Summon 1 "Ojama Token" (Beast / LIGHT / 2 Stars / ATK 0 / DEF 1000). That Token cannot be Tributed for a Tribute Summon. This Ability can only be used during your Main Phase.
(Ignition) Ojama Replacement
Tribute 2 "Ojama Token"s. Special Summon 1 "Ojama Black", "Ojama Green" or "Ojama Yellow" from your Deck. This Ability can only be used during your Main Phase.
Old Vindictive Magician
(Ignition) Sage Vindication
Tribute 1 monster and select 1 monster your opponent controls. Destroy the selected monster. When you activate this Ability, your opponent can pay 900 Life Points to negate the effect of this Ability. This Ability can only be used once per turn during your Main Phase.
Oppressed People
(Ignition) It's A Revolution!
Special Summon as many Monster Cards that are in your Deck Master Position as possible (except your Deck Master). This Ability can only be used during your Main Phase 2.
(Ignition) The Underground Movement
Put 1 "Oppressed People", "People Running About" or "United Resistance" from your hand in your Deck Master Position. This Ability can only be used once per turn during your Main Phase.
Orca Mega–Fortress of Darkness
(Continuous) Tidal Surge
All "Torpedo Fish" and "Cannonball Spear Shellfish" on the field gain 900 ATK and DEF.
Otohime
(Ignition) Shifting Stance
Select 1 face-up monster your opponent controls. Change the battle position of the selected monster. Your opponent cannot manually change the battle position of that monster during their next turn. This Ability can only be used once per turn during your End Phase.
(Continuous) Obnoxious Resistance
Monsters you control whose ATK is lower than or equal to 1400 cannot be destroyed by battle when they battle with monsters whose ATK is greater than or equal to 1900. (Damage calculation is applied normally.)
Ocean Dragon Lord – Neo-Daedalus
(Ignition) Raging Tidal Splash
Send 1 "Umi" in your hand or that you control to the Graveyard. Send up to 3 cards on the field and/or randomly from your opponent's hand to the Graveyard. This Ability can only be used during your Main Phase.
(Continuous) Water Default
While there is no face-up Field Spell Card on the field, this Ability is active. You are considered to control "Umi". All Fish, Sea Serpent, Thunder and Aqua-Type monsters on the field gain 200 ATK and DEF. All Machine and Pyro-Type monsters on the field lose 200 ATK and DEF.
Ocean's Keeper
(Continuous) Umi Stronghold
While you control "Umi", this Ability is active. "Umi" cannot be destroyed by a card effect. All Fish, Sea Serpent, Thunder and Aqua-Type monsters on the field gain 200 ATK and DEF. All Machine and Pyro-Type monsters on the field lose 200 ATK and DEF.
Ojama King
(Ignition) Ojama Reinforcement
Pay 500 Life Points. Special Summon 1 "Ojama Token" (Beast / LIGHT / 2 Stars / ATK 0 / DEF 1000). That Token cannot be Tributed for a Tribute Summon. This Ability can only be used during your Main Phase.
(Ignition) Ojama Replacement
Tribute 2 "Ojama Token"s. Special Summon 1 "Ojama Black", "Ojama Green" or "Ojama Yellow" from your Deck. This Ability can only be used during your Main Phase.
Old Vindictive Magician
(Ignition) Sage Vindication
Tribute 1 monster and select 1 monster your opponent controls. Destroy the selected monster. When you activate this Ability, your opponent can pay 900 Life Points to negate the effect of this Ability. This Ability can only be used once per turn during your Main Phase.
Oppressed People
(Ignition) It's A Revolution!
Special Summon as many Monster Cards that are in your Deck Master Position as possible (except your Deck Master). This Ability can only be used during your Main Phase 2.
(Ignition) The Underground Movement
Put 1 "Oppressed People", "People Running About" or "United Resistance" from your hand in your Deck Master Position. This Ability can only be used once per turn during your Main Phase.
Orca Mega–Fortress of Darkness
(Continuous) Tidal Surge
All "Torpedo Fish" and "Cannonball Spear Shellfish" on the field gain 900 ATK and DEF.
Otohime
(Ignition) Shifting Stance
Select 1 face-up monster your opponent controls. Change the battle position of the selected monster. Your opponent cannot manually change the battle position of that monster during their next turn. This Ability can only be used once per turn during your End Phase.