Mortal Shell 2: How to Get the Serpent Stone Poison Tarstone

The Serpent Stone is the Tarstone in Mortal Shell 2 that puts Poison on your weapon. It spends Resolve to coat your strikes, and Poison then chips away at an enemy’s health over time. At 15 Resolve, it is the cheapest infusion in the game, and once fully upgraded the effect never wears off.

Quick answer: Defeat Lucian, the Thirsting Knight inside The Hidden Keep dungeon, reached by resting at the Stonebled Gate beacon and cleansing it. He drops the Serpent Stone when he dies.

Serpent Stone effects and upgrade levels

The Serpent Stone is an Infusion Tarstone that slots into your primary weapon. Its core action spends 15 Resolve to imbue the weapon with Poison. Each upgrade extends how long that infusion holds, ending in a version that never expires.

Level	Effect
Base	Consume 15 Resolve to infuse your weapon with Poison
Level 1	Infusion lasts for 4 strikes
Level 2	Infusion lasts for 8 strikes
Level 3	Infusion is permanent

Poison drains enemy HP gradually rather than in one hit. Some foes resist it and some are weak to it, so it pays off most on tougher targets that survive long enough for the damage to stack. Because it only costs 15 Resolve, roughly half of what most infusions ask, you can keep it running without starving your sidearm of Resolve.

The stone fits two weapons: the Axe and Dagger, and the Black Needle. Equip it to your primary weapon through the equipment menu, then activate the infusion in combat to spend the Resolve.

Inventory menu highlighting an equippable Seal and its listed effects — Tarstones and Seals are equipped from the inventory menu before you head into the fight. Image credit: Cold Symmetry

Route to The Hidden Keep

The Serpent Stone sits at the end of a short dungeon run that starts from the Widow’s Overlook beacon and finishes at the Stonebled Gate. Follow the path below to reach the boss arena.

Fast travel to the Widow’s Overlook beacon and head out through Blackridge Cliffs. Poison mechanics are already relevant here, so any weapon that accepts the stone is worth carrying.

Player character crossing a rocky canyon in Blackridge Cliffs with the combat HUD on screen — The run begins in the rocky canyon of Blackridge Cliffs, just past the Widow’s Overlook beacon. Image credit: Cold Symmetry

Continue through Blackridge Pass toward the Sanguine Caverns portal. A bone spider blocks part of the route here, so clear it before moving on.

Warrior running along a narrow sunlit rock path in Blackridge Pass — Blackridge Pass narrows to a single rocky trail that leads to the Sanguine Caverns portal. Image credit: Cold Symmetry

Take the traversal portal into Sanguine Caverns and work your way deeper. A secret room here holds a Glimpse, and a Synaptic Vessel can be looted further in, both worth grabbing on the way through.

Armored character crossing a wooden bridge inside the icy Sanguine Caverns — A wooden bridge spans the icy interior of Sanguine Caverns on the way to Stonebled Gate. Image credit: Cold Symmetry

Reach and activate the Stonebled Gate beacon. Rest here and cleanse the beacon to open the way into The Hidden Keep dungeon.

Enter The Hidden Keep and push down the hallway, breaking through walls and fighting the guards inside. At the end of the hall, turn right into a dead-end room and press the plate to the left of the hole to reveal a new area.

The Hidden Keep area title appears inside a dark ruined stone interior — The Hidden Keep opens up after you cleanse the Stonebled Gate beacon. Image credit: Cold Symmetry

Cross the bridge, clearing the enemies along it. A Bloodseed can be looted on the way across. Step into the ring at the far side to start the boss fight.

Beating Lucian, the Thirsting Knight

Lucian is a two-phase mini-boss. The first phase is a straightforward duel in the arena. The catch comes in the second phase, when he retreats and turns much harder to see.

Fight Lucian normally until his health drops. He throws attacks at range, so close the gap and punish his recovery windows to burn down the first phase.

Player character striking Lucian with a sword during the boss fight in the ruined arena — Lucian, the Thirsting Knight, opens the fight as a standard duel before fleeing. Image credit: Cold Symmetry

Once he flees to an upper area, follow him through the teleporter, then squeeze through the gap in the wall on the left side. He becomes nearly invisible in the dark chamber, so track his movement carefully.

Finish the second phase to defeat Lucian completely. He drops the Serpent Stone along with a Glimpse and Gloom.

You will know the pickup succeeded when the Serpent Stone appears in your Tarstone inventory. After the fight, collect the three Ova eggs and cleanse the beacon to open the Corrupted Gate and continue onward.

Upgrading the Serpent Stone at the Tarforge

Tarstones level up at the Tarforge in Marrow Keep, but the Serpent Stone’s upgrade options only open once Franz has the Etching Needles. That quest item expands what the Tarforge can do.

The Etching Needles are looted from a chest right before the Magdalena, the Lady of the Woods boss fight. When you see Ruk past the bridge, drop down through the opening and turn right before the tunnel to reach a small section with a bone chest. Loot it to claim the Needles, then hand them to Franz.

With the Needles delivered, equip the Serpent Stone and defeat enemies to build its experience. Once the XP bar fills, return to Franz to buy the next upgrade level, which costs Coin each time. Push it all the way to the final level and the Poison infusion becomes permanent, letting you leave it running for the rest of a fight without spending Resolve again.