The Tenebris Somnia final boss is whichever of the two finale bosses your branch leads to — Lacuna or Hermes — and a third fight waits in the church on the street for the hidden ending. Your weapon is the Aurifer, and on the sparing branch Julia loses it when the fight starts.

Getting to Séptimo Arte

Both branches are reached the same way:

  1. From the hotel rooms, go south to the production-company lobby.
  2. Climb the main staircase to Floor 3.
  3. Take the left-hand door to the street.
  4. Walk left into the Séptimo Arte building.
  5. Inspect the sealed door at the far end.
  6. Walk back toward the entrance and speak with Vitria to start the finale.

Which of the two finales you meet depends on the branch you earned, and the endings guide explains how that branch is set.

Lacuna: the SOLVE ET COAGULA finale

Lacuna attacks with tentacles.

  1. Use the Revolver or Shotgun and hit her from outside her tentacle range.
  2. When she disappears, keep moving so her landing attack misses.
  3. During the mouth-swarm attack move close to her, because that is where the flies' spread does not reach you.
  4. In the second phase the cinema screen shows attacking doubles of Julia that you have to kill.
  5. Lacuna leaves a damaging trail across the arena while she is moving, so keep circling rather than standing still.
  6. Kill the flies that come out of the screen with a quick hit, dodge the stream of flies, and keep shooting in the openings until the ending triggers.

A hidden achievement is unlocked by dying to her grab attack: she leaps high into the air, and you have to stand still and let her snatch you.

Hermes: the Tenebris Somnia final boss of the MAGNUM OPUS ending

Hermes summons hands out of the floor, and each emergence point is marked with a symbol on the ground.

  1. Attack the hands with the Aurifer or a firearm.
  2. Watch for the eye's flash before each vertical or horizontal blast.
  3. Between rounds the movie screen previews the sweeping pattern of the next hand, so move into a gap before it crosses the arena.
  4. The rounds escalate from one attacker to two and then three.
  5. In the second phase a giant face comes out of the screen. Retreat when it inhales, because being pulled into its mouth kills Julia, then approach and attack once the inhaling stops and withdraw before the next cycle.
  6. Avoid the red eruptions on the floor, kill the small summons, keep clear of the emerging hands, and finish Hermes with the Aurifer once it is weakened.

A hidden achievement is unlocked by being eaten by Hermes in that second phase: walk into the exposed mouth on purpose.

The church fight for VIVUS EX MORTIBUS

A third finale fight happens in the church on the street, and it is only reachable with the three Iron Crosses.

  1. Julia fights a possessed woman alongside a priest named John.
  2. Stay away from her lunges and green projectiles.
  3. Kill the red creatures she summons.
  4. Attack her between summons with the Pipe or Revolver.
  5. John fights beside you, so leave him room to move.
  6. After John falls, avoid the spikes while you finish the pentagram phase.
  7. When the arena turns into a dark pentagram, keep moving through the gaps between the spikes and out of the projectile path. The three Iron Crosses that open the way to the church are in the secret ending guide.