Is it possible for a creature to drop an ITEMCORPSE in addition to its normal corpse? Failing that, is there some way to mod in a body part that will leave a gem when the critter is butchered? I guess some use of pearls might work, but there's nothing on the wiki about how to actually make pearls.
You can mod in a body part that will leave behind a butchery product that can be turned into gems automatically via reactions.
For example, in the material raws:
[MATERIAL_TEMPLATE:SMALL_SOUL_TEMPLATE]
[STATE_COLOR:ALL:PEARL]
[DISPLAY_COLOR:7:0:1]
[MATERIAL_VALUE:1]
[SPEC_HEAT:7500]
[MELTING_POINT:25000]
[BOILING_POINT:50000]
[SOLID_DENSITY:200]
[LIQUID_DENSITY:2600]
[MOLAR_MASS:55845]
[IMPACT_YIELD:5000000]
[IMPACT_FRACTURE:5000000]
[IMPACT_STRAIN_AT_YIELD:0]
[COMPRESSIVE_YIELD:5000000]
[COMPRESSIVE_FRACTURE:5000000]
[COMPRESSIVE_STRAIN_AT_YIELD:0]
[TENSILE_YIELD:5000000]
[TENSILE_FRACTURE:5000000]
[TENSILE_STRAIN_AT_YIELD:0]
[TORSION_YIELD:5000000]
[TORSION_FRACTURE:5000000]
[TORSION_STRAIN_AT_YIELD:0]
[SHEAR_YIELD:5000000]
[SHEAR_FRACTURE:5000000]
[SHEAR_STRAIN_AT_YIELD:0]
[BENDING_YIELD:5000000]
[BENDING_FRACTURE:5000000]
[BENDING_STRAIN_AT_YIELD:0]
[MAX_EDGE:1000]
[IMPLIES_ANIMAL_KILL]
[BUTCHER_SPECIAL:MEAT:NONE]
[MEAT_NAME:vanishing:soul:soul]
[MATERIAL_REACTION_PRODUCT:SMALL_SOUL_EXTRACT:NONE:NONE] Here, I'm saying I want this "soul" material to be part of a material reaction product.
Then in the body raws:
[BODY:SMALL_SOUL]
[BP:SMALL_SOUL:soul:STP][CONTYPE:UPPERBODY][INTERNAL][CATEGORY:SOUL] Just placing it arbitrarily in the body. INTERNAL marks it to be inside, and I should put a SMALL tag too.
[DEFAULT_RELSIZE:150]
Then in the tissue raws:
[TISSUE_TEMPLATE:SMALL_SOUL_TISSUE_TEMPLATE]
[TISSUE_NAME:soul:NP]
[STRUCTURAL]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:SMALL_SOUL] I'm saying that this tissue will be made out of the SMALL_SOUL material.
[RELATIVE_THICKNESS:2]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
Then in the b_detail:
[BODY_DETAIL_PLAN:STANDARD_MATERIALS_TOHO]
[ADD_MATERIAL:SKIN:SKIN_TEMPLATE]
[ADD_MATERIAL:FAT:FAT_TOHO_TEMPLATE]
[ADD_MATERIAL:MUSCLE:MUSCLE_TEMPLATE]
[ADD_MATERIAL:BONE:BONE_TEMPLATE]
[ADD_MATERIAL:CARTILAGE:CARTILAGE_TEMPLATE]
[ADD_MATERIAL:HAIR:HAIR_TEMPLATE]
[ADD_MATERIAL:TOOTH:TOOTH_TEMPLATE]
[ADD_MATERIAL:EYE:EYE_TEMPLATE]
[ADD_MATERIAL:NERVE:NERVE_TEMPLATE]
[ADD_MATERIAL:BRAIN:BRAIN_TEMPLATE]
[ADD_MATERIAL:LUNG:LUNG_TEMPLATE]
[ADD_MATERIAL:HEART:HEART_TEMPLATE]
[ADD_MATERIAL:LIVER:LIVER_TEMPLATE]
[ADD_MATERIAL:GUT:GUT_TEMPLATE]
[ADD_MATERIAL:STOMACH:STOMACH_TEMPLATE]
[ADD_MATERIAL:PANCREAS:PANCREAS_TEMPLATE]
[ADD_MATERIAL:SPLEEN:SPLEEN_TEMPLATE]
[ADD_MATERIAL:KIDNEY:KIDNEY_TEMPLATE]
[ADD_MATERIAL:LEATHER:LEATHER_TOHO_TEMPLATE]
[ADD_MATERIAL:TALLOW:TALLOW_TEMPLATE]
[ADD_MATERIAL:SOAP:SOAP_TEMPLATE]
[ADD_MATERIAL:ELEMENTAL:ELEMENTAL_TEMPLATE]
[ADD_MATERIAL:SMALL_SOUL:SMALL_SOUL_TEMPLATE] You don't really have to do this, but it just makes my life easier if I want to propagate this soul material to all the creatures. I'm adding this material to the creature file that calls up this template. I need to call up this material so I can use it.
[BODY_DETAIL_PLAN:STANDARD_TISSUES_TOHO]
[ADD_TISSUE:SKIN:SKIN_TEMPLATE]
[ADD_TISSUE:FAT:FAT_TEMPLATE]
[ADD_TISSUE:MUSCLE:MUSCLE_TEMPLATE]
[ADD_TISSUE:BONE:BONE_TEMPLATE]
[ADD_TISSUE:CARTILAGE:CARTILAGE_TEMPLATE]
[ADD_TISSUE:HAIR:HAIR_TEMPLATE]
[ADD_TISSUE:TOOTH:TOOTH_TEMPLATE]
[ADD_TISSUE:EYE:EYE_TEMPLATE]
[ADD_TISSUE:NERVE:NERVE_TEMPLATE]
[ADD_TISSUE:BRAIN:BRAIN_TEMPLATE]
[ADD_TISSUE:LUNG:LUNG_TEMPLATE]
[ADD_TISSUE:HEART:HEART_TEMPLATE]
[ADD_TISSUE:LIVER:LIVER_TEMPLATE]
[ADD_TISSUE:GUT:GUT_TEMPLATE]
[ADD_TISSUE:STOMACH:STOMACH_TEMPLATE]
[ADD_TISSUE:PANCREAS:PANCREAS_TEMPLATE]
[ADD_TISSUE:SPLEEN:SPLEEN_TEMPLATE]
[ADD_TISSUE:KIDNEY:KIDNEY_TEMPLATE]
[ADD_TISSUE:ELEMENTAL:ELEMENTAL_TEMPLATE]
[ADD_TISSUE:HORN:HORN_TEMPLATE_TOHO]
[ADD_TISSUE:SMALL_SOUL_TISSUE:SMALL_SOUL_TISSUE_TEMPLATE] Same here, I just did it for ease. I'm adding this tissue to the creature file that calls up this template.
[BODY_DETAIL_PLAN:SOUL_LAYER]
[BP_LAYERS:BY_TOKEN:SMALL_SOUL:SMALL_SOUL_TISSUE:100] I'm saying the soul body part is made out of the small soul tissue, which is made out of the small soul material, which has the reaction product...
[BODY_DETAIL_PLAN:SOUL_POSITIONS]
[BP_RELATION:BY_CATEGORY:RIB_TRUE:AROUND:BY_CATEGORY:SOUL:5]
[BP_RELATION:BY_CATEGORY:RIB_FALSE:AROUND:BY_CATEGORY:SOUL:5]
[BODY_DETAIL_PLAN:SOUL_RELSIZE]
[BP_RELSIZE:BY_TOKEN:SMALL_SOUL:100]
Then in the reaction raws:
[REACTION:SMALL_SOUL_EXTRACT]
[NAME:calm small soul]
[BUILDING:SOUL_SHRINE:CUSTOM_S]
[REAGENT:A:1:NONE:NONE:NONE:NONE]
[HAS_MATERIAL_REACTION_PRODUCT:SMALL_SOUL_EXTRACT] When you butcher it, and the soul is large enough, you'll butcher out the small soul, and then it will automatically be processed via this reaction. The material reaction product calls for the small soul material. Since this body part is the only thing using the soul material, you'll only ever use the butchery product to make the gem.
[PRODUCT:100:1:INSTRUMENT:ITEM_INSTRUMENT_SOUL:INORGANIC:SMALL] Change this to whatever gem you'd like. Also, note that I used a separate inorganic material called "SMALL" to create the reagent. This is to make it easier to call up this product in other reactions that will use this product as a reagent, and it prevents looping, where the product has the same material reaction as the regent, causing the reaction to take its own product as the reagent over and over.
[SKILL:PACIFY]
[AUTOMATIC]
Everything in green is ultimately the important parts. Also, everything relating to the material can be done inside the creature file. Messing with the body detail plans just makes it easier to save the shanges to all the animals. This is a pretty convoluted way, but I wanted to try and make sure that you'd only get around 1 soul per creature, which I can do by simply changing the relsize of the soul body part in the creature raw.
A far more elegant method is presented here:
http://www.bay12forums.com/smf/index.php?topic=80240.msg2285215#msg2285215