If the Core boss is still alive
You can return to your last save pool by letting the boss kill you. This method requires a living boss; it is not a return route for the state after you have defeated it.
- Make sure the boss is still alive.
- Let the boss defeat you.
- Resume from your last save pool.
Immortal run warning
Immortal requires finishing the game without dying. Using the death-return method conflicts with that goal. Consider your achievement run before choosing it.