Add this after [BODY_DETAIL_PLAN:STANDARD_TISSUES].
[TISSUE:BRONZE]
[TISSUE_NAME:bronze:bronze]
[TISSUE_MATERIAL:INORGANIC:BRONZE]
[MUSCULAR]
[FUNCTIONAL]
[STRUCTURAL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:ALL:BRONZE]
Switch out other metals if you want, but bronze is usually more than enough.
Bonus animal:
[CREATURE:CATOPLEBAS]
[DESCRIPTION:A huge, ill-tempered bovine with poisonous breath and bronze skin.]
[NAME:catopleblas:catopleblases:catopleblas]
[CHILD:1][GENERAL_CHILD_NAME:catopleblas calf:catopleblas calves]
[CREATURE_TILE:'C'][COLOR:6:0:0]
[BIOME:ANY_TEMPERATE_FOREST]
[BIOME:GRASSLAND_TEMPERATE]
[POPULATION_NUMBER:10:20]
[CLUSTER_NUMBER:5:10]
[PETVALUE:2000]
[PRONE_TO_RAGE:15]
[PREFSTRING:terrifying nature]
[LARGE_ROAMING][EVIL][SAVAGE]
[LIKES_FIGHTING][LARGE_PREDATOR][PET]
[BODY:QUADRUPED_HOOF:TAIL:2EYES:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:THROAT:NECK:SPINE:BRAIN:SKULL:MOUTH:GENERIC_TEETH:RIBCAGE:2HEAD_HORN]
[FANCIFUL]
[BODY_DETAIL_PLAN:STANDARD_MATERIALS]
[USE_MATERIAL_TEMPLATE:HOOF:HOOF_TEMPLATE]
[USE_MATERIAL_TEMPLATE:HORN:HORN_TEMPLATE]
[BODY_DETAIL_PLAN:STANDARD_TISSUES]
[USE_TISSUE_TEMPLATE:HOOF:HOOF_TEMPLATE]
[USE_TISSUE_TEMPLATE:HORN:HORN_TEMPLATE]
[TISSUE:BRONZE]
[TISSUE_NAME:bronze:bronze]
[TISSUE_MATERIAL:INORGANIC:BRONZE]
[MUSCULAR]
[FUNCTIONAL]
[STRUCTURAL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:ALL:BRONZE]
[HAS_NERVES]
[USE_MATERIAL_TEMPLATE:BLOOD:BLOOD_TEMPLATE]
[BLOOD:LOCAL_CREATURE_MAT:BLOOD:LIQUID]
[CREATURE_CLASS:GENERAL_POISON]
[GETS_WOUND_INFECTIONS]
[GETS_INFECTIONS_FROM_ROT]
[USE_MATERIAL_TEMPLATE:PUS:PUS_TEMPLATE]
[PUS:LOCAL_CREATURE_MAT:PUS:LIQUID]
[BODY_SIZE:0:0:100000]
[BODY_SIZE:1:0:500000]
[BODY_SIZE:2:0:1000000]
[BODY_APPEARANCE_MODIFIER:LENGTH:90:95:98:100:102:105:110]
[BODY_APPEARANCE_MODIFIER:HEIGHT:90:95:98:100:102:105:110]
[BODY_APPEARANCE_MODIFIER:BROADNESS:90:95:98:100:102:105:110]
[MAXAGE:100:200]
[USE_MATERIAL_TEMPLATE:CGAS:CREATURE_EXTRACT_TEMPLATE]
[STATE_NAME:ALL_SOLID:frozen catopleblas saliva]
[STATE_ADJ:ALL_SOLID:frozen catopleblas saliva]
[STATE_NAME:LIQUID:catopleblas spit]
[STATE_ADJ:LIQUID:catopleblas spit]
[STATE_NAME:GAS:catopleblas breath]
[STATE_ADJ:GAS:catopleblas breath]
[MELTING_POINT:9950]
[BOILING_POINT:10000]
[PREFIX:NONE]
[SYNDROME]
[SYN_NAME:catoplebas breath]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[SYN_IMMUNE_CREATURE:CATOPLEBAS:ALL]
[SYN_INHALED]
[CE_PARALYSIS:SEV:100:PROB:100:RESISTABLE:SIZE_DILUTES:START:5:PEAK:100:END:200]
[MATERIAL_BREATH_ATTACK:LOCAL_CREATURE_MAT:CGAS:TRAILING_GAS_FLOW]
[ATTACK:HGORE:BODYPART:BY_CATEGORY:HORN]
[ATTACK_SKILL:BITE]
[ATTACK_VERB:gore:gores]
[ATTACK_CONTACT_PERC:100]
[ATTACK_FLAG_WITH]
[ATTACK_PRIORITY:MAIN]
[ATTACK:KICK:BODYPART:BY_CATEGORY:HOOF_FRONT]
[ATTACK_SKILL:STANCE_STRIKE]
[ATTACK_VERB:kick:kicks]
[ATTACK_CONTACT_PERC:100]
[ATTACK_PRIORITY:SECOND]
[ATTACK_FLAG_WITH]
[ATTACK:KICK:BODYPART:BY_CATEGORY:HOOF_REAR]
[ATTACK_SKILL:STANCE_STRIKE]
[ATTACK_VERB:kick:kicks]
[ATTACK_CONTACT_PERC:100]
[ATTACK_PRIORITY:SECOND]
[ATTACK_FLAG_WITH]
[ATTACK:BITE:CHILD_BODYPART_GROUP:BY_CATEGORY:HEAD:BY_CATEGORY:TOOTH]
[ATTACK_SKILL:BITE]
[ATTACK_VERB:bite:bites]
[ATTACK_CONTACT_PERC:100]
[ATTACK_PENETRATION_PERC:100]
[ATTACK_FLAG_EDGE]
[ATTACK_PRIORITY:SECOND]
[ATTACK_FLAG_CANLATCH]
[DIURNAL]
[HOMEOTHERM:10068]
[SWIMS_INNATE][SWIM_SPEED:2500]
[MUNDANE]
[CASTE:FEMALE]
[CASTE_NAME:catopleblas cow:catopleblas cows:catopleblas cow]
[FEMALE]
[CASTE:MALE]
[CASTE_NAME:catopleblas bull:catopleblas bulls:catopleblas bull]
[MALE]
[SELECT_MATERIAL:ALL]
[MULTIPLY_VALUE:5]
I've pitted the cluster nuimber against armies of a hundred or so armed and armored humanoids in arena mode and watched them slaughter the lot. If anything, they're worse than a Bronze Colossus thanks to their ability to gore as well as bludgeon. I've seen them penetrate adamantine before with those horns.