Mortal Shell 2 Illusionist’s Cache Walkthrough (Illusion Arch Puzzle)

The Illusionist’s Cache is one of Mortal Shell 2’s optional dungeons, tucked into the Desolate Peak directly across from Baghead and his followers. Its core challenge is an illusion puzzle that rewrites the room around you depending on what you look at through a stone archway, and it trips up players who have never seen the trick before.

Quick answer: Look through the first illusion arch to swap the dead end for a new chamber and step through to make it real. Shoot the distant bell with your sidearm to spawn a bridge, cross the second illusion arch to replace the floor hole with solid ground, then push the movable pillar onto the pressure plate. Return through the arch one last time to open the sealed room and take the Shuddering Stone Tarstone.

Where to find the Illusionist’s Cache

The dungeon sits on the Desolate Peak, reached from north of the Outskirts of Nochte Beacon by using one of the Bone Gates. The entrance is inside the building, opposite the spot where Baghead rests on his throne. Before you drop in, grab the Crypt Key from the shelf just above the entrance, since it opens a door later on.

Take the elevator down to the lower level. You land in a narrow tunnel that ends in a wall, with two priest enemies waiting. Clear them out before you start on the puzzle.

How the illusion arch works

The whole dungeon runs on a single rule. When you look through an illusion arch, part of the room appears different, and when you physically step through that arch, the layout changes to match what you saw. Walls vanish, floors fill in, and passages open based on the view you passed through. You will use this to remove a bottomless hole and reset the room without losing your progress with the pillar.

Illusionist’s Cache puzzle solution

At the far end of the starting tunnel, destroy the stacked boxes next to the archway. This uncovers a short flight of stairs leading up to the first illusion arch.

Look through the arch. The dead-end wall at the end of the tunnel disappears, revealing a chamber farther ahead. Walk through the archway to make that view real and open the path forward.

In the next room, you will find a pressure plate, a hole in the floor, and a movable pillar on the far side of the hole. Stepping on the plate opens a chamber to your right, but it closes again the moment you step off. The goal is to weigh the plate down with the pillar.

Break the boxes beside the hole and attack the false wall behind them to open a new room. Two more priest enemies appear here, so defeat them before moving on.

Head up the stairs to the left and smash the breakable boxes at the top. A second illusion arch sits in front of you. You cannot reach it directly, but looking through it shows a metal bell on the other side.

Equip your sidearm and shoot the bell. A stone bridge appears, linking your ledge to the second illusion arch. If you are short on Resolve to fire, strike the Resolve-giving stalk next to you first.

Walk up and jump through the arch. The hole in the floor below is now replaced by solid concrete, so the gap no longer blocks the pillar.

Move behind the movable pillar and attack it to push it straight onto the pressure plate in the center of the room. The chamber the plate controls now shows a wall in front of it, which is expected.

Go back up the stairs and step through the illusion arch once more. This resets the room to its earlier state, with the hole restored and the wall removed. Because the pillar is holding the plate down, the hole no longer matters.

Enter the newly open room and open the chest to claim the Shuddering Stone Tarstone.

You know it worked when the “New Tarstone Acquired: Shuddering Stone” prompt appears. This Tarstone makes your projectiles generate a Knockback shockwave on impact.

Extra rewards and hidden rooms

Attack the fake wall behind the chest to open a small room, which hides yet another fake wall. Break through it to find a lone priest enemy and some Dorsalite, a weapon upgrade material.

Before you leave, take the elevator next to the stairs down and kill the snake enemy nesting there. You can collect a Ventrium and a Laterite from this area.

Reward	Where to get it
Shuddering Stone Tarstone	Chest in the room unlocked by the pressure plate
Dorsalite (upgrade material)	Behind the fake walls past the chest
Ventrium and Laterite	Down the elevator by the stairs, past the snake enemy
Crypt Key	Shelf above the dungeon entrance

With the Tarstone and side loot collected, the Illusionist’s Cache is complete, and you are free to head back up the elevator. Keep the Crypt Key on you, as it unlocks a door tied to the Hall of Echoes dungeon later in your run.