It's not my turn anymore, but made something based on my contagious disease stuff. Thoughts on adding?
c_variation_vampire_halfling
[OBJECT:CREATURE_VARIATION]
[CREATURE_VARIATION:HAS_VAMPIRES_HLG]
[CV_NEW_TAG:CAN_DO_INTERACTION:VAMPIRISM_FREQUENCY_REDUCER_HLG]
[CV_NEW_TAG:CDI:TARGET:A:SELF_ONLY]
[CV_NEW_TAG:CDI:WAIT_PERIOD:1200]
[CV_NEW_TAG:CDI:FREE_ACTION]
[CV_NEW_TAG:CDI:ADV_NAME:Pray to dark gods for vampirism]
interaction_vampire_halfling
[OBJECT:INTERACTION]
[INTERACTION:VAMPIRISM_FREQUENCY_REDUCER_HLG]
##needed to set a vampirism % < 1 ##
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:CAN_LEARN]
[IT_CANNOT_HAVE_SYNDROME_CLASS:VAMPIRISM_DETERMINED_1]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[SYNDROME]
[SYN_CLASS:VAMPIRISM_DETERMINED_1]
[SYN_NAME:vampirism present for creature]
[CE_CAN_DO_INTERACTION:PROB:10:START:0:END:9001]
[CDI:INTERACTION:VAMPIRISM_SWITCH_HLG]
[CDI:TARGET:A:SELF_ONLY]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:90001]
[CE_BODY_APPEARANCE_MODIFIER:APPEARANCE_MODIFIER:BROADNESS:99:START:0]
[INTERACTION:VAMPIRISM_SWITCH_HLG]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:CAN_LEARN]
[IT_CANNOT_HAVE_SYNDROME_CLASS:VAMPIRISM_DETERMINED_2]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[SYNDROME]
[SYN_NAME:vampirism determined]
[SYN_CLASS:VAMPIRISM_DETERMINED_2]
[CE_CAN_DO_INTERACTION:PROB:1:START:0:END:9001]
[CDI:INTERACTION:VAMPIRISM_HLG]
[CDI:TARGET:A:SELF_ONLY]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:90001]
[CE_BODY_APPEARANCE_MODIFIER:APPEARANCE_MODIFIER:BROADNESS:99:START:0]
[INTERACTION:VAMPIRISM_HLG]
[I_SOURCE:DEITY]
[IS_USAGE_HINT:MAJOR_CURSE]
[IS_HIST_STRING_1: cursed ]
[IS_HIST_STRING_2: with a dark desire to feast on the blood and souls of their loved ones!]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:CAN_LEARN]
[IT_CANNOT_HAVE_SYNDROME_CLASS:VAMPIRISM]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[IE_ARENA_NAME:Vampire HLG]
[SYNDROME]
[SYN_NAME:is a vampire!]
[SYN_CLASS:VAMPIRISM]
## vanilla vampirism except vampires DO eat and drink so as to avoid the alcohol dependence stupidity,
do gain and rust in physical attributes and are attacked by undead ##
[CE_ADD_TAG:BLOODSUCKER:NO_AGING:NOEXERT:NOPAIN:NOBREATHE:NOSTUN:NONAUSEA:NO_DIZZINESS:NO_FEVERS:PARALYZEIMMUNE:NO_SLEEP:START:0]
[CE_PHYS_ATT_CHANGE:STRENGTH:200:0:AGILITY:200:0:TOUGHNESS:200:0:START:0]
## after one year, vampires can and will turn another suitable creature into a vampire
2x/year ##
[CE_CAN_DO_INTERACTION:START:403200]
[CDI:INTERACTION:VAMPIRISM_HLG]
[CDI:TARGET:A:TOUCHABLE]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:201600]
[CDI:ADV_NAME:Spread vampirism]
## when threatened, vampires can become incredibly dangerous 1x/day ##
[CE_CAN_DO_INTERACTION:START:0]
[CDI:INTERACTION:VAMPIRE_ATTACK_HLG]
[CDI:TARGET:A:SELF_ONLY]
[CDI:USAGE_HINT:FLEEING]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:1200]
[CDI:ADV_NAME:Release your hidden strength!]
[CE_DISPLAY_TILE:TILE:165:5:0:1:START:0:CAN_BE_HIDDEN]
[CE_DISPLAY_NAME:NAME:vampire:vampires:bloodsucker:START:0:CAN_BE_HIDDEN]
[INTERACTION:VAMPIRE_ATTACK_HLG]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[SYNDROME]
[SYN_NAME:is suffused with dark power!]
[CE_ADD_TAG:CRAZED:LIKES_FIGHTING:START:0:END:300]
## values may seem absurdly high but they just max it for the creature ##
[CE_PHYS_ATT_CHANGE:STRENGTH:100000:100000:START:0:END:300]
[CE_PHYS_ATT_CHANGE:AGILITY:100000:100000:START:0:END:300]
[CE_SPEED_CHANGE:SPEED_PERC:1000:START:0:END:300]
## increases strength more, enough to visibly propel creatures away ##
[CE_BODY_APPEARANCE_MODIFIER:APPEARANCE_MODIFIER:HEIGHT:1000:START:0:END:300]
[CE_CAN_DO_INTERACTION:START:0:END:300]
[CDI:INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Vampiric cloud]
[CDI:MATERIAL:INORGANIC:DARK_BLOOD_HLG:UNDIRECTED_GAS]
[CDI:WAIT_PERIOD:1200]
[CDI:USAGE_HINT:ATTACK]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:VERB:are surrounded by a cloud of darkness:is surrounded by a cloud of darkness:na]
inorganic_vampire_halfling
[OBJECT:INORGANIC]
[INORGANIC:DARK_BLOOD_HLG]
[USE_MATERIAL_TEMPLATE:BLOOD_TEMPLATE_HLG]
Description: Any sentient creature can be cursed into becoming a famous vampire. To make vampirism more common, you can add creature variation HAS_VAMPIRES to creature - that makes 0.1% of that creature's population be unidentifiable "unnamed" vampires that don't have a history you could screen for. Vampires suck blood and receive physical attribute boosts, but unlike in vanilla they still eat and drink to avoid any stupidity with alcohol dependence and they do gain physical attributes with training. They are also not allied with the undead. Vampirism is properly contagious - if a vampire is present in your fort for one year, they will start converting other sentients present into vampires at a rate of 2 per year. If a vampire is threatened (fleeing), they may release a cloud of "dark blood" and gain insane physical attribute boosts for a few in-game seconds, going berserk for the time and trying to kill anybody nearby. This results in limbs flying and blood spraying a lot, and actually makes them strong enough to tear apart a storm dragon. But they will go for anybody nearby first when scared, so this is supposed to be pretty bad for you, but can be weaponized with some effort.
That last part can easily be removed if it seems excessive.
Edit: Alt version where they turn into a small and fast flying vampire bat instead when threatened:
creature_vampire_halfling
[OBJECT:CREATURE]
[CREATURE:VAMPIRE_BAT_HLG]
[DESCRIPTION:A small, bloodsucking creature. It is associated with night and darkness.]
[NAME:vampire bat:vampire bats:bloodsucker]
[CASTE_NAME:vampire bat:vampire bats:bloodsucker]
[CREATURE_TILE:'w'][COLOR:0:0:0]
[PREFSTRING:thirst for blood]
[PREFSTRING:dainty little fangs]
[PREFSTRING:appeal to their dark and poetic soul, and they would prefer you not to laugh]
[NATURAL_SKILL:BITE:15]
[NATURAL_SKILL:DODGING:15]
[CREATURE_CLASS:ALL][CREATURE_CLASS:FLYING][BIOME:ANY_LAND][FREQUENCY:5]
[CREATURE_CLASS:MAMMAL][CREATURE_CLASS:VERTEBRATE]
[FANCIFUL][NOCTURNAL][FLIER][TRAPAVOID][OPPOSED_TO_LIFE]
[PETVALUE:0]
[SPEED:300]
[HAS_NERVES][GETS_WOUND_INFECTIONS][GETS_INFECTIONS_FROM_ROT][HOMEOTHERM:10070]
[SWIMS_INNATE][SWIM_SPEED:3000]
[BODY_SIZE:2000]
[BODY_SIZE:0:0:2000]
[BODY:CORE_HLG:BACK_LEGS_HLG:BIRD_ARMS_HLG:EXTERNAL_EARS_HLG:TAIL_HLG:TEETH_HLG]
[BODY_DETAIL_PLAN:CORE_MATERIALS_HLG]
[BODY_DETAIL_PLAN:CORE_TISSUES_HLG]
[BODY_DETAIL_PLAN:CORE_LAYERS_HLG]
[BODY_DETAIL_PLAN:TEETH_HLG]
[BODY_DETAIL_PLAN:BACK_LEGS_LAYERS_HLG]
[BODY_DETAIL_PLAN:BIRD_ARMS_LAYERS_HLG]
[BODY_DETAIL_PLAN:EXTERNAL_EARS_LAYERS_HLG]
[BODY_DETAIL_PLAN:TAIL_LAYERS_HLG]
[BODYGLOSS:TWOLEGS_HLG]
[BODYGLOSS:CLAWTOES_HLG]
[SELECT_MATERIAL:ALL]
[MULTIPLY_VALUE:0]
[TENDONS:LOCAL_CREATURE_MAT:TENDON:400]
[LIGAMENTS:LOCAL_CREATURE_MAT:TENDON:400]
[BLOOD:LOCAL_CREATURE_MAT:BLOOD:LIQUID]
[APPLY_CREATURE_VARIATION:SCRATCH_CLAW_HLG]
[APPLY_CREATURE_VARIATION:APPEARANCE_VARIABILITY_EYE_COLOR_HLG]
[APPLY_CREATURE_VARIATION:APPEARANCE_VARIABILITY_BODYSIZE_HLG]
[ATTACK:BITE:BODYPART:BY_CATEGORY:TOOTH]
[ATTACK_SKILL:BITE]
[ATTACK_VERB:bite:bites]
[ATTACK_CONTACT_PERC:100]
[ATTACK_PENETRATION_PERC:100]
[ATTACK_FLAG_EDGE]
[ATTACK_PRIORITY:MAIN]
[ATTACK_FLAG_CANLATCH]
[SPECIALATTACK_SUCK_BLOOD:50:100]
[CASTE:MALE][MALE]
[CASTE:FEMALE][FEMALE]
interaction_vampire_halfling
[OBJECT:INTERACTION]
[INTERACTION:VAMPIRISM_FREQUENCY_REDUCER_HLG]
##needed to set a vampirism % < 1 ##
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:CAN_LEARN]
[IT_CANNOT_HAVE_SYNDROME_CLASS:VAMPIRISM_DETERMINED_1]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_CLASS:VAMPIRISM_DETERMINED_1]
[SYN_NAME:vampirism present for creature]
[CE_CAN_DO_INTERACTION:PROB:10:START:0:END:9001]
[CDI:INTERACTION:VAMPIRISM_SWITCH_HLG]
[CDI:TARGET:A:SELF_ONLY]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:90001]
[CE_BODY_APPEARANCE_MODIFIER:APPEARANCE_MODIFIER:BROADNESS:99:START:0]
[INTERACTION:VAMPIRISM_SWITCH_HLG]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:CAN_LEARN]
[IT_CANNOT_HAVE_SYNDROME_CLASS:VAMPIRISM_DETERMINED_2]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_NAME:vampirism determined]
[SYN_CLASS:VAMPIRISM_DETERMINED_2]
[CE_CAN_DO_INTERACTION:PROB:1:START:0:END:9001]
[CDI:INTERACTION:VAMPIRISM_HLG]
[CDI:TARGET:A:SELF_ONLY]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:90001]
[CE_BODY_APPEARANCE_MODIFIER:APPEARANCE_MODIFIER:BROADNESS:99:START:0]
[INTERACTION:VAMPIRISM_HLG]
[I_SOURCE:DEITY]
[IS_USAGE_HINT:MAJOR_CURSE]
[IS_HIST_STRING_1: cursed ]
[IS_HIST_STRING_2: with a dark desire to feast on the blood and souls of their loved ones!]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:CAN_LEARN]
[IT_CANNOT_HAVE_SYNDROME_CLASS:VAMPIRISM]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[IE_ARENA_NAME:Vampire HLG]
[SYNDROME]
[SYN_NAME:is a vampire!]
[SYN_CLASS:VAMPIRISM]
## vanilla vampirism except vampires DO eat and drink so as to avoid the alcohol dependence stupidity,
do gain and rust in physical attributes and are attacked by undead ##
[CE_ADD_TAG:BLOODSUCKER:NO_AGING:NOEXERT:NOPAIN:NOBREATHE:NOSTUN:NONAUSEA:NO_DIZZINESS:NO_FEVERS:PARALYZEIMMUNE:NO_SLEEP:START:0]
[CE_PHYS_ATT_CHANGE:STRENGTH:200:0:AGILITY:200:0:TOUGHNESS:200:0:START:0]
## after one year, vampires can and will turn another suitable creature into a vampire
2x/year ##
[CE_CAN_DO_INTERACTION:START:403200]
[CDI:INTERACTION:VAMPIRISM_HLG]
[CDI:TARGET:A:TOUCHABLE]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:201600]
[CDI:ADV_NAME:Spread vampirism]
## when threatened, vampires can become incredibly dangerous 1x/day ##
[CE_CAN_DO_INTERACTION:START:0]
[CDI:INTERACTION:VAMPIRE_ATTACK_HLG]
[CDI:TARGET:A:SELF_ONLY]
[CDI:USAGE_HINT:FLEEING]
[CDI:FREE_ACTION]
[CDI:MAX_TARGET_NUMBER:A:1]
[CDI:WAIT_PERIOD:1200]
[CDI:ADV_NAME:Transform into a bat and escape!]
[CE_DISPLAY_TILE:TILE:165:4:0:1:START:0:CAN_BE_HIDDEN]
[CE_DISPLAY_NAME:NAME:vampire:vampires:bloodsucker:START:0:CAN_BE_HIDDEN]
[INTERACTION:VAMPIRE_ATTACK_HLG]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_NAME:has taken the form of a bat!]
[CE_BODY_TRANSFORMATION:START:0:END:300]
[CE:CREATURE:VAMPIRE_BAT_HLG:FEMALE]
[CE_CAN_DO_INTERACTION:START:0:END:300]
[CDI:INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Vampiric cloud]
[CDI:MATERIAL:INORGANIC:DARK_BLOOD_HLG:UNDIRECTED_GAS]
[CDI:WAIT_PERIOD:1200]
[CDI:USAGE_HINT:ATTACK]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:VERB:are surrounded by a cloud of darkness:is surrounded by a cloud of darkness:na]