Here is the full list of all 60 The Elder Scrolls IV: Oblivion GotY (JP) achievements worth 1,250 gamerscore.
Completed the Dark Brotherhood Questline
Reached Speaker rank in the Dark Brotherhood
Reached Silencer rank in the Dark Brotherhood
Reached Assassin rank in the Dark Brotherhood
Reached Eliminator rank in the Dark Brotherhood
Reached Slayer rank in the Dark Brotherhood
Join the Dark Brotherhood
Completed the Thieves Guild Questline
Reached Master Thief rank in the Thieves Guild
Reached Shadowfoot rank in the Thieves Guild
Reached Cat Burglar rank in the Thieves Guild
Reached Prowler rank in the Thieves Guild
Reached Bandit rank in the Thieves Guild
Reached Footpad rank in the Thieves Guild
Joined the Thieves Guild
Completed the Mages Guild Questline
Reached Master-Wizard rank in the Mages Guild
Reached Wizard rank in the Mages Guild
Reached Warlock rank in the Mages Guild
Reached Magician rank in the Mages Guild
Reached Conjurer rank in the Mages Guild
Reached Evoker rank in the Mages Guild
Reached Journeyman rank in the Mages Guild
Reached Apprentice rank in the Mages Guild
Joined the Mages Guild
Completed the Main Questline
Destroyed the Great Gate, Main Quest
Delivered Daedric Artifact, Main Quest
Located the Shrine of Dagon, Main Quest
Closed an Oblivion Gate, Main Quest
Completed the Arena Questline
Reached Champion rank in the Arena
Reached Hero rank in the Arena
Reached Gladiator rank in the Arena
Reached Warrior rank in the Arena
Reached Myrmidon rank in the Arena
Reached Bloodletter rank in the Arena
Reached Brawler rank in the Arena
Joined the Arena in the Imperial City
Completed the Fighters Guild Questline
Reached Champion rank in the Fighters Guild
Reached Guardian rank in the Fighters Guild
Reached Warder rank in the Fighters Guild
Reached Defender rank in the Fighters Guild
Reached Protector rank in the Fighters Guild
Reached Swordsman rank in the Fighters Guild
Reached Journeyman rank in the Fighters Guild
Reached Apprentice rank in the Fighters Guild
Joined the Fighters Guild
Stopped the Greymarch
Reached Defender of the Realm Rank in the Court of Madness
Reached Regent Rank in the Court of Madness
Reached Duke of Mania Rank in the Court of Madness
Reached Duke of Dementia Rank in the Court of Madness
Reached Honored Madman Rank in the Court of Madness
Reached Madman Rank in the Court of Madness
Reached Citizen Rank in the Court of Madness
Reached Aspirant Rank in the Court of Madness
Entered the Shivering Isles
Escaped the Imperial Sewers, Main Quest Beginning