Mortal Shell 2: How to Get the Infested Stone Tarstone

The Infested Stone turns the Ballistazooka into a delayed demolition tool. Instead of a straight blast, it fires a projectile that latches onto whatever it hits and detonates a moment later. Getting it does not involve a dungeon, a boss, or a hidden chest — it is a straight purchase, but from a merchant who only exists while the world is in Night.

Quick answer: Speak to Thestus in Marrow Keep and pay 1 Glimpse for “Call Forth the Night,” then fast travel to the Abandoned Outpost beacon in the Deserted Slums and buy the Infested Stone from The Collector for 1,500.

What the Infested Stone does

The Infested Stone is an Ability Tarstone, which means it slots into a sidearm rather than a melee weapon or a shell. It is locked to the Ballistazooka, so if you are not carrying that sidearm the stone has nowhere to go. Firing it costs Resolve and produces a clinging projectile that sticks in place before exploding.

Like every Tarstone, it gains levels as you kill enemies with it equipped, and each level layers on a new property rather than simply raising a number.

Level	Effect
1	Spends Resolve to fire a clinging projectile that detonates in a large explosion after a short delay
2	The projectile deals 100 damage when it explodes
3	The projectile pulls the aggression of every nearby enemy
4	The explosion scatters 3 additional clinging projectiles

To fire it once equipped, hold the sidearm aim button and press the heavy attack — on a controller, hold L2 then press R2. The aggro pull at level 3 is worth noting, since a stone stuck to a wall or a corpse will drag a group toward it and away from you before it goes off.

Sidearm slot highlighted on the HUD as the character fights an enemy on a narrow bridge — The Infested Stone fires from the sidearm slot and sticks before detonating. Image: Cold Symmetry

Before you go: what you need

Two resources gate the purchase, and both are easy to check from the menu before you make the trip.

1 Glimpse — the cost of summoning the night at Marrow Keep.
1,500 Tar — the price of the stone itself. The Collector’s other stones cost the same each, so bring more if you plan to clear his stock.
The Ballistazooka — not required to buy the stone, but you cannot equip it without that sidearm.

Summon the night at Marrow Keep

Fast travel to Marrow Keep and make your way through the hub to Thestus. He is the NPC who controls the day and night cycle, and nothing about the Collector works until you talk to him.

Armored Harbinger climbing wooden stairs inside Marrow Keep on the way to Thestus — Cutting through Marrow Keep toward Thestus, who handles the night cycle. Image: Cold Symmetry

Speak to him and choose “Call Forth the Night.” It costs 1 Glimpse. The screen confirms the change with a “Night Summoned” message, and the lighting across the world shifts accordingly.

Note: if the option does not appear or you cannot pay for it, you are short a Glimpse. Pick one up before returning — the trip is pointless without the night active.

Reach The Collector in the Deserted Slums

Open the fast travel map and select the Outskirts of Mammon beacon. That is the closest convenient landing point if you have not yet unlocked the beacon further in.

Run south-east from Outskirts of Mammon toward the Deserted Slums. It is a short stretch of open ground and you can simply sprint past most of what spawns along the way.

Player running forward along a wooden walkway between the Outskirts of Mammon and the Deserted Slums — The run from Outskirts of Mammon into the Deserted Slums. Image: Cold Symmetry

Light the Abandoned Outpost beacon when you reach it. This becomes your fast travel point for any return visits, which matters because you will likely come back for the rest of his stock.

On-screen prompt to hold E to use the Gloom Siphon at a beacon — Interact at the beacon to bank your progress before hunting down the merchant. Image: Cold Symmetry

From the beacon, walk out into the surrounding slums and look for The Collector. He is close by, standing in the dark rather than inside any building, so sweep the immediate area rather than wandering far.

Character walking a dark rocky path in the Deserted Slums toward a glowing point of light — The Collector waits a short walk from the Abandoned Outpost beacon, only while the night is active. Image: Cold Symmetry

Open his trade menu, find the Infested Stone in his inventory, and buy it for 1,500. The stone lands in your Tarstones menu straight away.

Everything else The Collector sells

Since the Collector only appears at night and the trip costs a Glimpse each time, it is worth clearing his shelf in one visit. Three other Tarstones sit alongside the Infested Stone at the same price.

Tarstone	Type	Price
Infested Stone	Ability	1,500
Fulminant Stone	Ability	1,500
Infused Stone	Ability	1,500
Weeping Stone	Infusion	1,500

He also deals in materials such as Thoracium and Tarcore, plus the Blackarrow Key.

If The Collector is not there

There are only a couple of reasons the merchant fails to show, and both are fixable in a minute.

The night is not active. The Collector exists only while Night is summoned. If the world looks like daytime, go back to Thestus and pay the Glimpse.
You are searching too wide an area. He stands near the Abandoned Outpost beacon, not deeper in the Deserted Slums.
You cannot afford him. The stone is a flat 1,500 with no discount.

Levelling the Infested Stone at the Tarforge

Upgrades run through Franz at the Tarforge in Marrow Keep, but he cannot touch a Tarstone until you hand him the Etching Needle. That quest item sits in a bone chest shortly before the fight with Magdalena, the Lady of the Woods. When you spot Ruk past the bridge, drop through the opening and turn right before the tunnel to find the small alcove holding it.

After that, each level needs two things. Keep the stone equipped and kill enemies until its experience bar fills, then pay Franz to push it to the next level. Levels are not required to use the stone, and they are not needed for the Stoned trophy either — the game asks for 73 of the 75 Tarstones, not upgraded ones.

You will know the purchase stuck the moment the Infested Stone shows up in the Ability section of your Tarstones menu. Slot it into the Ballistazooka, take it into a group of enemies, and the level-3 aggro pull becomes the reason to keep it equipped long after the novelty of the explosion wears off.