Immundus

Immundus is the family of crystals that the host body grows when Sendrils drain it. In game terms they are the talent currency: every level of every talent costs exactly one stone of a fixed tier, spent at an Altar (see Altars and Leveling). There are five tiers, listed here from cheapest to rarest. Tier 5, the Sea Tooth Bone, belongs to the DLC hero Jerold and is the only tier that is not a crystal.

The five tiers#

Picking up any stone completes quest 12017 (ItemData CompleteQuestId); the game uses that flag to decide whether the item is new to you (inferred).

How stones are spent#

Each talent row stores a StoneLevel list with one tier per level, for example "3,4" means level 1 costs an Immundus Crystal and level 2 costs an Immundus Diamond. Confirming a talent consumes one stone of that tier per level bought. Tiers are not interchangeable: a Diamond cannot pay for a Chipped slot.

Total stones to buy every talent that does not start unlocked (counted from HeroTalent.StoneLevel; talents flagged DefaultOpen are free):

A talent flagged DefaultOpen starts at level 1 for free, so only its levels 2 and up are counted (the first entry of its StoneLevel list is skipped). That matters for Elena, whose starting talent Demiurge's Curse (StoneLevel 1,2,4) still costs one tier-2 and one tier-4 stone for its extra levels. See Terrence talent tree, Viola talent tree, Benita talent tree, Norwood talent tree, Jerold talent tree and Elena talent tree for which talent costs what.

Where the stones come from#

Stones are not a normal enemy drop. Almost all of them are placed in the world or sold, and the supply per playthrough is fixed.

Ground pickups (main chapters 1-9)#

Counts are the number of stones placed in each New Game Plus journey (StoryItem, columns ItemId_1 to ItemId_4 are the four journeys).

The pickups shift toward higher tiers as you replay: Chipped Immundus on the ground dwindles from 20 to 7, Immundus rises from 34 to 41, and the rare tiers stay put. Chapter 1 (Heggem) has only 2 Chipped Immundus on the ground in the first journey and none in later ones. All 13 Sea Tooth Bones (12 spots) are in the Ichthyosauria DLC chapter, and 6 more are sold there.

Dark Mist stages (story ids 101-105)#

The five Dark Mist stages hold a few more ground pickups: 4 Chipped, 3 Immundus, 3 Crystal and 1 Diamond in the first journey, then 5, 5, 3 and 1 from the second journey on. See Deep into the Dark Mist.

Merchants#

Every chapter's merchants sell stones. Stock is limited and is not restocked by resting (IsRefresh is 0); it resets only when a new journey begins. The full stock lists are in Chapter merchants. Per merchant, first journey:

Prices by journey (journey 1 / journey 2 / journey 3 / journey 4 or later):

Crystals and Diamonds are priced in the higher currencies, not in Bone Fragments, so you cannot just grind Bone Fragments for them. Fractured Bodies do not drop from enemies at all, only from pickups (see Currencies#Big Bone, Fractured Body and Filthy Core pickups per journey (chapters 1-9)).

Changing shop slots. A shop row has four columns, one per journey, and a column may hold a different item. The Chipped Immundus slot at Heggem (row 11002) and the Chipped slots at Adamina (20001), Exilium (30001) are Chipped Immundus only in the first journey. From journey 2 on, those same slots sell Blackwater Debris at 185 / 275 / 405 Bone Fragments. If you are planning stone purchases in New Game Plus, buy talents from the Edith and later merchants.

Enemy and boss drops#

Drop tables (ItemDropData) contain only a handful of stone entries:

Six more groups pay 100% (Immundus x2 in chapter 2, Crystal in chapters 3 and 5, Diamond in chapters 4, 6 and 7) but no monster row in the data points at them, so they are probably boss rewards wired another way or leftovers (inferred).

No talent raises these odds (see Lucky Madness in the Hidden mechanics below).

Hidden mechanics#

• You cannot max everyone in one run. The visible supply in the first journey (ground + merchants + Dark Mist stages) is about 64 Chipped, 64 Immundus, 31 Crystal, 12 Diamond and 19 Sea Tooth Bone, against a full five-hero bill of 26 / 86 / 81 / 28 / 19 (Elena's Arcade tree is separate). Immundus, Crystals and Diamonds are the bottleneck; the rest is made up over New Game Plus journeys (see New Game Plus). Jerold's bill of 19 Sea Tooth Bones matches the 13 pickups plus 6 merchant stock exactly, so a full Jerold tree needs every single one.
• Shop prices rise every journey. The same stone costs about 3.3 times as much in journey 4 as in journey 1 (20 to 65, 50 to 165).
• In Dance of the Throne (Arcade) stones turn into time. When you pick up a stone in Arcade mode, it is swapped for a hidden "time reduction" item (ids 72001-72004, internal Chinese names only) that shortens your run clock by 30 s (Chipped), 60 s, 90 s or 120 s (Diamond) per stone. This always happens for every hero except Elena. Elena keeps real stones, but only until all her talents' stone needs of that tier are met (IsTalentStoneEnough). In stage-select mode the swap always applies. Sea Tooth Bone has no swap. See Arcade mode. (The unit of the 30-120 value is seconds, inferred from SubGameTime.)
• Lucky Madness does not help. Each hero's talent 405 Lucky Madness adds 5 / 10 to the weight of drop entries, but only for the item types it names (Terrence 701 and 706, Viola 801 and 803, Benita 802 and 702, Norwood and Jerold 601-603), at any sanity; the rule is in Drops and loot#Talent bonus: Lucky Madness and Materials#hm-lucky-madness-talent-talent-405-adds-5-level. Stones are type 501, which no hero lists, so the talent never touches them.
• Not sellable. Stones have price -1, so the merchant sell screen never lists them.
• Limited stack. A stack holds 99; extra pickups are lost and the game prints "bag is full" (AddBagItem).

Sources#

• ES_ItemData rows 50001-50005 (MainType 5, Type 501, NumMax 99, CompleteQuestId 12017); luascript/structdata/ms_itemdata.lua:47-57,130-137.
• ES_HeroTalent StoneLevel column, recounted by build/wiki/scripts/verify_items_b/v13.py; ui/controller/playerinfoctrl.lua:4283-4300 (next level looks up LevelList[level]), :4825-4925 (confirm and spend); structdata/fs_talentdata.lua:41 (DefaultOpen talents start at level 1).
• ES_StoryItem columns ItemId_1..4 / Num_1..4 (journeys via MS_StoryItem.SetLoop, structdata/ms_storyitem.lua:28-40, fs_savestory.lua:1956-1979, BattleData.GameLoopMax = 4 at logic/battle/battledata.lua:45).
• ES_TransactionData rows 11002, 20001-20002, 30001, 31002, 40001-40002, 41002, 50001-52002, 60001-61003, 70001-71002, 90001-93003; refresh rules ms_transactiondata.lua:43-62, fs_savestory.lua:3419-3450.
• ES_ItemDropData groups 10010, 10018, 70002, 70008, 90002, 90012 (and the six unreferenced groups); roll code controller/controllerstorymode.lua:5355-5417.
• Arcade swap: logic/item/itemscene.lua:34-45, controller/controllerstorymode.lua:5558-5563; ItemData 72001-72004 Param1 30/60/90/120.
• Talent 405: ES_HeroTalent ids 11403, 12403, 13403, 14403, 15403 (Type 43 = ItemProbAdd).