How many endings does Tenebris Somnia have?

Destructoid lists four: Solve Et Coagula, Magnum Opus, Vivus Ex Mortibus and Renuntiatio, with the first two as the good and bad endings of one run.

How do I get the good ending?

Pick up the Aurifer knife and leave every Relicta ghost alive, which Destructoid calls the Solve Et Coagula ending.

What locks in the bad ending?

Killing at least one Relicta ghost with the Aurifer hands Julia the Magnum Opus ending, and further kills stay optional.

Do the other two endings need a new game?

Yes. Vivus Ex Mortibus asks for both main endings first and then a new game, and Renuntiatio is reached the same way.

What does the Bible do in Tenebris Somnia?

Using it on the Man/Mars symbol six times, opening the 6666 lock with it and using it on Floor 0 opens the Vivus Ex Mortibus route.

Tenebris Somnia Endings: All Four and How to Unlock Them

How many endings Tenebris Somnia has

Destructoid lists four endings: Solve Et Coagula, Magnum Opus, Vivus Ex Mortibus and Renuntiatio. The first pair is the good and bad ending of a single run, and both are settled by what Julia does once the Aurifer knife is in the inventory. The other two only open on a new game started after the first pair has been seen.

Story spoiler · what happens to Julia in the two main endings

TV Tropes calls the two main endings bittersweet. One leaves Julia reunited with Iván and facing Sanguis and the Relicta afterwards; the other has her break away from Iván's abuse, end the Relicta for good and still carry the memories of the ordeal. That second route closes with at least three dead Relictas, Vitria among them. Renuntiatio skips the confrontation and leaves the cult's plan unfinished.

How the Aurifer splits the good and bad ending

TV Tropes describes the Aurifer as an ordinary melee weapon against anything with a body, but a permanent kill against a Relicta in spirit form. That second property is the whole ending switch, and it is also why the ghosts back away from Julia instead of attacking her.

Reach the Aurifer knife and keep it in the inventory.
Leave every Relicta spirit alive on the way back for Solve Et Coagula.
Stab one Relicta spirit with the Aurifer to lock in Magnum Opus instead.

Tenebris Somnia screenshot Official Steam screenshot

Destructoid reports the ghosts trying to avoid Julia out of fear once the knife is hers, so the good route needs no kill at all and the bad one is settled by the first stab. How many later kills follow is left to the player.

How to unlock Vivus Ex Mortibus

The Bible is the key item for this ending, and each use has a deadline: the TV puzzle and the Copper Key door have to come after it. Destructoid orders the run as follows.

Finish Solve Et Coagula and Magnum Opus, then start a new game.
Take the Bible from the desk.
On the second floor of the apartment, use the Bible, start on the Man/Mars symbol and run counterclockwise six times, before the TV puzzle is solved.
On the first floor of the Community Center, use the Bible and enter 6666 into the lock, without opening that lock any other way.
On Floor 0, go through the green door, use the Bible again, connect the yellow RCA cable to the camera and keep switching channels until enemies spawn, before the door that opens with the Copper Key.
On the third floor, enter the blue door left of the elevator, insert the three Iron Crosses and go through.

Story spoiler · where the Bible route ends

TV Tropes ties the Bible to FAITH, which Airdorf Games also produced: each use plays a brief rotoscoped animation in that style and offers a second solution to a puzzle. Three of those puzzles solved put Julia beside Father John Ward to finish his exorcism of Amy, and Ward's cross then carries into later playthroughs.

How to unlock Renuntiatio

Destructoid's instruction for the fourth ending is one action taken after the two main endings: use the apartment keys on the door.

Clear Solve Et Coagula and Magnum Opus.
Start a new game and get the apartment keys.
Use the apartment keys on the door.

Tenebris Somnia screenshot Official Steam screenshot

Story spoiler · why the keys decide the fourth ending

Tenebris Somnia is a curse attached to an object: touching it compels the holder to perform a set action. The apartment keys carry it for the whole game, forcing Julia to keep them but never to return to the apartment. Walking away without throwing them off therefore breaks the Relicta's plan before she learns there was one. The last Devora film reel carries the same curse and sends her to a distant room instead of the inventory.