The "1001%" achievement in The Binding of Isaac: Afterbirth (which serves as a foundational milestone for the Repentance expansion) is more than just a completion mark; it is a testament to a player’s mastery over one of the most complex roguelikes ever created. Achieving a "1001 Save File" signifies that a player has not only beaten every boss with every character but has also navigated the game’s deep pool of cryptic secrets and punishing RNG. The Trial of Persistence
If you are looking to skip the grind or recover progress, you can manually install a pre-completed save file following these steps from Steam Community guides and technical wikis : Binding Of Isaac Repentance 1001 Save File
Once you confirm the save works, close the game, re-enable Steam Cloud in Properties, and launch again. Choose "Upload to Cloud" when prompted (choose as the winner). The "1001%" achievement in The Binding of Isaac: