Tarstones do nothing extra until you can level them, and that whole system stays locked behind one key item in Mortal Shell 2. To turn on Tarstone tempering at the Tarforge, you need the Etching Needles and a quick trip back to Franz in Marrow Keep.
Quick answer: Grab the Etching Needles from a chest in the Glutted Mire (the Corrupted Gate dungeon in southeast Fainweald), right after the Tarblighted Shepherd boss and just before the Magdalena fight. Hand them to Franz at the Tarforge to unlock the “Temper Tarstones” option. Killing Franz unlocks the same option instantly with no downside.
Where to find the Etching Needles in the Glutted Mire
The Etching Needles sit inside the Glutted Mire, the Corrupted Gate dungeon on the eastern side of the map, next to the Mushroom Village Gate Beacon. The chest is unguarded, so this is a fast pickup once you reach it.
Note: Because this chest is right before a major boss, treat the Etching Needles as your cue to head back to Marrow Keep before pushing into Magdalena’s arena.
Unlock Temper Tarstones at the Tarforge
The Tarforge lives in Marrow Keep, right next to Franz the Tarforge Smith, and it is reachable through Beacons once fast travel is available. Two paths unlock Tarstone tempering.
There is a shortcut if you would rather skip the errand. Killing Franz in Marrow Keep instantly unlocks all four Tarforge functions at once, including Temper Tarstones, with no penalty to the services the forge offers. If you kill him and later bring the Etching Needles anyway, the forge simply rewards you with crafting materials instead of unlocking anything new.
How Tarstone tempering works: XP, coins, and Tarcores
Tempering raises a Tarstone through its four levels, and each level strengthens its passive effect or unlocks a transformed version of it. Before you can spend anything, though, the stone needs experience.
A Tarstone only gains XP while it is slotted into an equipped weapon or sidearm and you kill enemies. Leaving it in your inventory does nothing. Some Tarstones are also restricted to specific weapons, so a stone that will not slot into a given armament cannot earn XP there.
Once a stone hits its XP threshold, you finish the level-up at the Tarforge by paying the coin cost. The table below breaks down what each step needs.
| Upgrade step | Requirement |
|---|---|
| Level 1 to Level 2 | 10,000 XP on the stone, then 100 coins at the Tarforge (grants 1 Tarcore) |
| Next threshold to max | 20,000 XP reached, then 6 Tarcore spent to max the stone out |
| XP source | Kill enemies while the stone is slotted in an equipped weapon or sidearm |
| First Tarcore | Obtained after giving the Etching Needles to Franz or killing him |
Because maxing a favorite stone costs six Tarcores, the practical loop is to push many different Tarstones from Level 1 to Level 2. Each of those cheap 100-coin upgrades hands back a Tarcore, and you funnel that surplus into the stones you actually want at maximum.
How to confirm tempering is unlocked
You know it worked when the Tarforge menu shows “Temper Tarstones” as a selectable option and the first Tarcore appears in your inventory. Open the menu, pick a stone that has met its XP threshold, and confirm the level jumps from Level 1 to Level 2 after paying coins.
If a stone will not let you upgrade it, the usual reason is XP. Tarstones sitting in your inventory or slotted into a weapon you never use will stay stuck at Level 1 until you equip them and rack up kills. Keep the stones you care about in active loadouts, and the Tarcores will pile up as you clear the map.
