Quick answer
Tarstones are the main build-customization layer beyond your Shell and weapons. They fall into Support, Combat, Infusion and Ability roles. Some work globally; others only fit specific melee weapons or sidearms. Equipped Tarstones gain XP from kills and can later be tempered at the Tarforge once that function is unlocked.
The four practical Tarstone roles
Support: broad passive improvements that support the Harbinger/Shell plan.
Combat: modifiers tied more directly to weapon or sidearm performance.
Infusion: applies an elemental/status effect to compatible equipment.
Ability: adds a specific active/special move to a compatible weapon or sidearm.
The point is modularity: the same Shell can become a different build by changing the melee weapon, sidearm, compatible stones and the status effect you are trying to trigger.
Compatibility matters
Not every Tarstone fits every weapon. If a build guide says “use this stone” but it does not light up as compatible with your current weapon/sidearm, the guide may be describing a different equipment pair or an old patch interaction.
Full-release build testing repeatedly shows the best setups coming from one coherent interaction, not from stacking the four highest-looking numbers.
Tarstone XP
Equipped Tarstones gain experience while you kill enemies. Current Tarforge guides report that the stone needs to be slotted on equipment you actually have equipped for the XP loop to work.
You do not need to activate an effect on every kill just to earn XP.
Tempering is a separate unlock
The Tarforge in Marrow Keep does not expose every function immediately. Current launch routes tie Tarstone tempering to the Etching Needles (or an alternate aggressive shortcut involving Franz that this site does not recommend as the default path).
See Tarstone Tempering for the upgrade route.
Balance Patch 1 changed Tarstones already
The first balance post explicitly buffs several stones, including Parasitic, Grudge, Bulwark, Clerik’s and Squall. That makes one point unavoidable: Tarstone tier lists are patch-sensitive.
Build Tarstones around the Shell loop
Examples from full-release testing:
- Eredrim: support Break/riposte frequency, Resolve generation and the weapon’s best stagger window.
- Genessa: reinforce Phantom stacking, multi-hit attacks and safe summon pressure.
- Proxima: support Shock/Lightning interactions rather than generic damage alone.
The Shell should tell you what question the Tarstones need to answer.