To unlock the Past Mistakes trophy in Assassin's Creed Odyssey, you simply need to complete the game's second episode.
Assassin's Creed Odyssey Episode 2 Quests:
- Learning the Ropes
- Equal Employment Opportunity Program
- A Journey into War
- The Athenian Leader
- Crumble and Burn
- The Athenian Treasure Trove
- The Final Push
- The Wolf of Sparta