Successfully complete the campaign to unlock Original Game Plus mode. In this mode, Billie's powers are replaced with fully upgraded versions of the Dark Vision, Blink, and Domino powers from Dishonored 2.
Good ending: After interacting with the black eye in the cave halfway through Mission 5, you will enter the void. From the eye, turn around and look for a corpse on some spikes. Loot the key from the corpse to trigger the "Inspect Malchiodi's Lodging" optional objective. Mark it in your quest log and disable the markers for other objectives to see it more easily. The marker will guide you to a room that can be opened using the key. Inside the room is a chest. The key code is 962. Read the book from the chest to complete the objective. Then, proceed to the main objective (go to the Ritual Hold). When you reach the Outsider, create a manual save. You can reload this later to get the bad ending. Inspect the Outsider's body (press Square), then talk to Daud a few times. Always choose the non-lethal dialogue option to let the Outsider live. After talking to Daud a few times, he will walk over to the Outsider and release him. You will then get the good ending and the "Final Release" trophy.
Bad ending: For the bad ending, you do not have to do the optional objective. Once you reach the Outsider, simply perform a melee attack on him to instantly kill him and get the bad ending and the "Deicide" trophy. If you created a manual save during the good ending, you can reload it after the final cutscene.
Twin-bladed Knife (25 points): Obtain an ancient weapon.
Golden Locks (30 points): Steal the audiograph from the gallery without disabling the safeguard floor.
Nightingale (30 points): Use Semblance to mimic Shan Yun and sing into the microphone.
Public Shaming (30 points): Drop Ivan Jacobi through the trapdoor.
Big-time Player (30 points): Win the auction at Colibron Plaza.
Obsessive Safe-cracker (30 points): Open every safe inside the main vault.
The Perfect Crime (30 points): Empty the vault without tampering with any security systems, leaving everyone unharmed and asleep.
Party Crasher (30 points): Send the vault crashing through the floor.
The Face of the Abbey (30 points): Attend the meeting as Brother Cardoza.
Voices (30 points): Break 4 Oraculum censers and listen to the prophecies.
Harder than Stone (30 points): Destroy an Envisioned cultist.
Final Nudge (20 points): Push an enemy to his demise using Void Strike.
Hooked (40 points): Send someone flying 40 meters using Hook Mines.
Mightier than the Sword (20 points): Shoot a guard in the head with a fountain pen.
Clever Planning (20 points): Use Displace on a marker placed with Foresight and eliminate a target.
Salute! (20 points): Have a guard salute you.
Rat Whisperer (20 points): Listen to what swarms of rats have to say 5 times.
Shadow (100 points): Finish the game without being detected.
Agent of Mercy (20 points): Finish a mission without killing anyone.
Good Old Times (50 points): Finish the Original Game+.
Side Effects (20 points): Make 3 people vomit using a single bottle of Plagued Spirit.
Occupational Hazard (20 points): Make an enemy explode into pieces using Displace.
Mercenary Work (75 points): Complete all contracts (Bronze): (Art Aficionado (50 points): Collect all Eleuterio Cienfuegos paintings.
Uncaged (25 points): Free the assassin Daud.
Two Turns (25 points): Take both bank vault keys.
Gnosis (25 points): Recover the stolen archive.
Dead Eye (25 points): Touch the Eye of the Dead God.
Final Release (50 points): Return the Outsider to the mortal world.
Deicide (50 points): Kill the Outsider.