Defeat Lavos and obtain any of the 12 original endings.
This new dungeon has three parts to it and can only be unlocked when you've completed the game by defeating Lavos.
|Lost Sanctum||Unlock the Black Omen|
|Ending #1 "Beyond Time"||Defeat Lavos after reviving Crono at Death Peak.|
|Ending #10 "Dino age"||Defeat Lavos after facing Magus, but before facing Azala.|
|Ending #11 "What The Prophet Seeks"||Defeat Lavos after facing Azala, but before Schala opens the sealed door.|
|Ending #12 "Memory lane"||Defeat Lavos after Schala opens the sealed door, but before restoring the light to the pendant.|
|Ending #13 "Dream's Epilogue"||Defeat the Dream Devourer beyond Time's Eclipse|
|Ending #2 "Reunion"||Defeat Lavos while Crono is dead.|
|Ending #3 "The Dream Project"||Defeat Lavos in the Ocean Palace or immediately upon starting a new game +.|
|Ending #4 "The successor of Guardia"||Defeat Lavos after saving Leene and Marle, but before visiting the End of Time.|
|Ending #5 "Good Night"||Defeat Lavos after visiting the End of Time, but before returning to the Middle ages.|
|Ending #6 "The Legendary Hero"||Defeat Lavos after arriving in the middle ages, but before obtaining the Hero's Badge.|
|Ending #7 "The Unknown Past"||Defeat Lavos after obtaining the Hero's Badge, but before the Gate key is stolen.|
|Ending #8 "People of the times"||Defeat Lavos after regaining the gate key, but before giving the Masamune to Frog.|
|Ending #9 "The Oath"||Defeat Lavos after giving the Masamune to Frog but before fighting Magus|