I have completed my creature. I call it the Dark Rider. It is basically equivalent to the grim reaper mounted on a horse, complete with bloodsucking scythe.
Here is the creature file
[CREATURE:DARK_RIDER]
[NAME:dark rider:dark riders:darkened]
[TILE:21][COLOR:0:5:0]
[INTELLIGENT][FANCIFUL]
[ALL_ACTIVE][SAVAGE][EVIL]
[GRASSTRAMPLE:0][MEGABEAST]
[ENDING][POWER]
[PREFSTRING:death-dealing]
[PREFSTRING:skeletal horses]
[PREFSTRING:scythes]
[PREFSTRING:dark cloaks]
[NO_DRINK][NO_EAT][NO_GENDER][NO_SLEEP][NOBLEED][NOEMOTION]
[NOEXERT][NOFEAR][NOMEAT][NONAUSEA][NOPAIN][NOSKIN][NOSMELLYROT]
[NOSTUCKINS][NOSTUN][NOT_BUTCHERABLE][PARALYZEIMMUNE][AMPHIBIOUS]
[BONECARN][BUILDINGDESTROYER:2][EXTRAVISION][FIREIMMUNE_SUPER]
[LIKES_FIGHTING][AMBUSHPREDATOR][LISP][MAGMA_VISION][STOUT]
[TRAPAVOID][UNDERSWIM][WEBIMMUNE]
[BODY:DARK_RIDER:DARK_RIDER_JOINTS:DARK_RIDER_DIGITS:SCYTHE]
[DAMBLOCK:5][SIZE:11][FAT:0]
[EXTRACT_PARALYZE]
[EXTRACT:fear:7:0:0]
[ATTACK:MAIN:BYTOKEN:SKULL:gaze at:gazes into:0:0:PIERCE][SPECIALATTACK_INJECT_EXTRACT:50:100]
[ATTACK:MAIN:BYTOKEN:SCYTHE:slash:slashes:5:10:SLASH][SPECIALATTACK_SUCK_BLOOD:100:250]
[ATTACK:MAIN:BYTOKEN:LH:touch:touches:3:5:COLD]
[ATTACK:MAIN:BYTYPE:STANCE:trample:tramples on top of:1:3:BLUDGEON]
[ATTACK:MAIN:BYTOKEN:HJAW:bite:bites into:1:3:GORE]
[ITEMCORPSE:ROUGH:NO_SUBTYPE:STONE:DEATH_CURSE]
[FIXED_TEMP:10010][COLDDAM_POINT:0][HEATDAM_POINT:19936]
[SPEED:500][SWIMS_INNATE][SWIM_SPEED:1000]
[BIOME:ANY_LAND]
[POPULATION_NUMBER:1:5]
[CLUSTER_NUMBER:1:1]
Here is the body tags.
[BODY:DARK_RIDER]
[BP:SPINE:spine][UPPERBODY][JOINT]
[BP:CLOAK:dark cloak][CON:SPINE]
[BP:RIBS:ribcage][CON:SPINE]
[BP:SKULL:skull][CON:SPINE][HEAD][THOUGHT]
[BP:NECK:neck][CON:SKULL][INTERNAL][JOINT][NERVOUS][SMALL]
[BP:REYE:right glowing eye][CON:SKULL][SMALL][RIGHT][EMBEDDED][SIGHT]
[BP:LEYE:left glowing eye][CON:SKULL][SMALL][LEFT][EMBEDDED][SIGHT]
[BP:JAW:jawbone][MOUTH][APERTURE][EMBEDDED][JOINT][SMALL]
[BP:RUA:right upper arm][CON:SPINE][RIGHT][LIMB]
[BP:LUA:left upper arm][CON:SPINE][LEFT][LIMB]
[BP:RLA:right lower arm][CON:RUA][RIGHT][LIMB]
[BP:LLA:left lower arm][CON:LUA][LEFT][LIMB]
[BP:RH:right skeletal hand][CON:RLA][RIGHT]
[BP:LH:left skeletal hand][CON:LLA][LEFT]
[BP:HIPS:pelvis][CON:SPINE]
[BP:RUL:right upper leg][CON:HIPS][RIGHT][LIMB]
[BP:LUL:left upper leg][CON:HIPS][LEFT][LIMB]
[BP:RLL:right lower leg][CON:RUL][RIGHT][LIMB]
[BP:LLL:left lower leg][CON:LUL][LEFT][LIMB]
[BP:RF:right skeletal foot][CON:RLL][RIGHT]
[BP:LF:left skeletal foot][CON:LLL][LEFT]
[BP:SADDLE:saddle][CON:HIPS][LOWERBODY]
[BP:HSPINE:horse's spine][CON:SADDLE]
[BP:HRIBS:horse's ribs][CON:HSPINE]
[BP:HSKULL:horse's skull][CON:HSPINE][SMELL]
[BP:HNECK:horse's neck][CON:SKULL][INTERNAL][JOINT][NERVOUS][SMALL]
[BP:HJAW:horse's jawbone][MOUTH][APERTURE][EMBEDDED][JOINT][SMALL]
[BP:HREYE:horse's right eye][CON:HSKULL][SMALL][RIGHT][EMBEDDED][SIGHT]
[BP:HLEYE:horse's left eye][CON:HSKULL][SMALL][LEFT][EMBEDDED][SIGHT]
[BP:HFRL:front right leg][RIGHT][CON:HSPINE]
[BP:HFLL:front left leg][LEFT][CON:HSPINE]
[BP:HFRF:front right hoof][CON:HFRL][RIGHT][STANCE]
[BP:HFLF:front left hoof][CON:HFLL][LEFT][STANCE]
[BP:HBRL:back right leg][RIGHT][CON:HSPINE]
[BP:HBLL:back left leg][LEFT][CON:HSPINE]
[BP:HBRF:back right hoof][CON:HFRL][RIGHT][STANCE]
[BP:HBLF:back left hoof][CON:HFLL][LEFT][STANCE]
[BODY:DARK_RIDER_JOINTS]
[BP:RUA_J:right shoulder][CON:RUA][RIGHT][JOINT][SMALL][INTERNAL]
[BP:LUA_J:left shoulder][CON:LUA][LEFT][JOINT][SMALL][INTERNAL]
[BP:RLA_J:right elbow][CON:RLA][RIGHT][JOINT][SMALL][INTERNAL]
[BP:LLA_J:left elbow][CON:LLA][LEFT][JOINT][SMALL][INTERNAL]
[BP:RH_J:right wrist][CON:RH][RIGHT][JOINT][SMALL][INTERNAL]
[BP:LH_J:left wrist][CON:LH][LEFT][JOINT][SMALL][INTERNAL]
[BP:RUL_J:right hip][CON:RUL][RIGHT][JOINT][SMALL][INTERNAL]
[BP:LUL_J:left hip][CON:LUL][LEFT][JOINT][SMALL][INTERNAL]
[BP:RLL_J:right knee][CON:RLL][RIGHT][JOINT][SMALL][INTERNAL]
[BP:LLL_J:left knee][CON:LLL][LEFT][JOINT][SMALL][INTERNAL]
[BP:RF_J:right ankle][CON:RF][RIGHT][JOINT][SMALL][INTERNAL]
[BP:LF_J:left ankle][CON:LF][LEFT][JOINT][SMALL][INTERNAL]
[BP:HFRL_J:front right hip][CON:HFRL][RIGHT][JOINT][SMALL][INTERNAL]
[BP:HFLL_J:front left hip][CON:HFLL][LEFT][JOINT][SMALL][INTERNAL]
[BP:HFRF_J:front right ankle][CON:HFRF][RIGHT][JOINT][SMALL][INTERNAL]
[BP:HFLF_J:front left ankle][CON:HFLF][LEFT][JOINT][SMALL][INTERNAL]
[BP:HBRL_J:back right hip][CON:HBRL][RIGHT][JOINT][SMALL][INTERNAL]
[BP:HBLL_J:back left hip][CON:HBLL][LEFT][JOINT][SMALL][INTERNAL]
[BP:HBRF_J:back right ankle][CON:HBRF][RIGHT][JOINT][SMALL][INTERNAL]
[BP:HBLF_J:back left ankle][CON:HBLF][LEFT][JOINT][SMALL][INTERNAL]
[BODY:DARK_RIDER_DIGITS]
[BP:LFINGER1:thumb][CON:LH][DIGIT][SMALL]
[BP:LFINGER2:1st finger][CON:LH][DIGIT][SMALL][JOINT]
[BP:LFINGER3:2nd finger][CON:LH][DIGIT][SMALL][JOINT]
[BP:LFINGER4:3rd finger][CON:LH][DIGIT][SMALL][JOINT]
[BP:LFINGER5:4th finger][CON:LH][DIGIT][SMALL][JOINT]
[BP:LTOE1:1st toe][CON:LF][DIGIT][SMALL][JOINT]
[BP:LTOE2:2nd toe][CON:LF][DIGIT][SMALL][JOINT]
[BP:LTOE3:3rd toe][CON:LF][DIGIT][SMALL][JOINT]
[BP:LTOE4:4th toe][CON:LF][DIGIT][SMALL][JOINT]
[BP:LTOE5:5th toe][CON:LF][DIGIT][SMALL][JOINT]
[BP:RFINGER1:thumb][CON:RH][DIGIT][SMALL]
[BP:RFINGER2:1st finger][CON:RH][DIGIT][SMALL][JOINT]
[BP:RFINGER3:2nd finger][CON:RH][DIGIT][SMALL][JOINT]
[BP:RFINGER4:3rd finger][CON:RH][DIGIT][SMALL][JOINT]
[BP:RFINGER5:4th finger][CON:RH][DIGIT][SMALL][JOINT]
[BP:RTOE1:1st toe][CON:RF][DIGIT][SMALL][JOINT]
[BP:RTOE2:2nd toe][CON:RF][DIGIT][SMALL][JOINT]
[BP:RTOE3:3rd toe][CON:RF][DIGIT][SMALL][JOINT]
[BP:RTOE4:4th toe][CON:RF][DIGIT][SMALL][JOINT]
[BP:RTOE5:5th toe][CON:RF][DIGIT][SMALL][JOINT]
[BODY:SCYTHE]
[BP:SCYTHE:scythe][CON:RH][BREATHE]
This also has to be added to the matgloss_stone_mineral.txt file
[MATGLOSS_STONE:DEATH_CURSE]
[NAME:death curse][COLOR:0:5:0][TILE:21]
[MELTING_POINT:0]
[BOILING_POINT:1]
[SOLID_DENSITY:1]
*Note for people: this stone allows the Dark Rider to unleash a freezing death curse when he dies, freezing nearby dwarves or other creatures in a boiling cloud.
And here is a picture showing somewhat what it looks like.