I'm not sure exactly how much these guys would fit into your mod, but if you want to, feel free to use them.
[CREATURE:FLAYL_SUNDER]
[NAME:sunder flayl:sunder flayls:sunder flayl]
[TILE:F][COLOR:0:0:1]
[MODVALUE:10]
[LARGE_ROAMING][DAMBLOCK:1]
[LARGE_PREDATOR][LIKES_FIGHTING][RECKLESS]
[NOFEAR][NOEXERT][NONAUSEA]
[FREQUENCY:3][FLIER][BONECARN]
[POPULATION_NUMBER:5:15]
[CLUSTER_NUMBER:1:1]
[PREFSTRING:collossal wings]
[PREFSTRING:strength]
[PREFSTRING:gaping maws]
[PREFSTRING:tentacles]
[BODY:FLAYL:2WINGS:4EYES:2TUSKS:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:5FINGERS:3TOES:MOUTH]
[BODYGLOSS:MAW]
[SIZE:9]
[ATTACK:MAIN:BYTYPE:MOUTH:bite:bites:1:6:GORE][ATTACKFLAG_CANLATCH]
[ATTACK:MAIN:BYTYPE:GRASP:punch:punches:1:2:BLUDGEON][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:RUTC:slash:slashes:1:4:SLASH][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:LUTC:slice:slices:1:4:SLASH][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:RLTC:stab:stabs:1:3:PIERCE][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:LLTC:strike:strikes:1:6:GORE][ATTACKFLAG_WITH]
[ALL_ACTIVE][NO_SLEEP]
[FAT:4]
[BIOME:MOUNTAIN]
[BIOME:SUBTERRANEAN_CHASM]
[BUTCHERABLE_NONSTANDARD]
[STANDARD_FLESH]
[HOMEOTHERM:10067]
[LAYERING:300]
[CREATURE:FLAYL_FROST]
[NAME:frost flayl:frost flayls:frost flayl]
[TILE:F][COLOR:7:0:0]
[MODVALUE:10]
[LARGE_ROAMING][FIREBREATH][FIREIMMUNE]
[LARGE_PREDATOR][LIKES_FIGHTING][RECKLESS]
[NOFEAR][NOEXERT][NONAUSEA]
[FREQUENCY:3][BONECARN]
[POPULATION_NUMBER:5:15]
[CLUSTER_NUMBER:1:1]
[PREFSTRING:pale grey skin]
[PREFSTRING:strength]
[PREFSTRING:gaping maws]
[PREFSTRING:tentacles]
[BODY:FLAYL:4EYES:2TUSKS:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:5FINGERS:3TOES:MOUTH]
[BODYGLOSS:MAW]
[SIZE:9]
[ATTACK:MAIN:BYTYPE:MOUTH:bite:bites:1:6:GORE][ATTACKFLAG_CANLATCH]
[ATTACK:MAIN:BYTYPE:GRASP:punch:punches:1:2:BLUDGEON][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:RUTC:slash:slashes:1:4:SLASH][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:LUTC:slice:slices:1:4:SLASH][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:RLTC:stab:stabs:1:3:PIERCE][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:LLTC:strike:strikes:1:6:GORE][ATTACKFLAG_WITH]
[ALL_ACTIVE][NO_SLEEP]
[FAT:4]
[BIOME:GLACIER]
[BIOME:TUNDRA]
[BIOME:FOREST_TAIGA]
[BUTCHERABLE_NONSTANDARD]
[STANDARD_FLESH]
[HOMEOTHERM:10067]
[LAYERING:300]
[SWIMS_INNATE][SWIM_SPEED:2500][AMPHIBIOUS]
[CREATURE:FLAYL_WASTE]
[NAME:waste flayl:waste flayls:waste flayl]
[TILE:F][COLOR:1:0:0]
[MODVALUE:10][SPEED:650]
[LARGE_ROAMING]
[LARGE_PREDATOR][LIKES_FIGHTING][RECKLESS]
[NOFEAR][NOEXERT][NONAUSEA]
[FREQUENCY:3][BONECARN]
[POPULATION_NUMBER:5:15]
[CLUSTER_NUMBER:1:1]
[PREFSTRING:speed]
[PREFSTRING:strength]
[PREFSTRING:gaping maws]
[PREFSTRING:tentacles]
[BODY:FLAYL:4EYES:2TUSKS:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:5FINGERS:3TOES:MOUTH]
[BODYGLOSS:MAW]
[SIZE:10]
[ATTACK:MAIN:BYTYPE:MOUTH:bite:bites:1:6:GORE][ATTACKFLAG_CANLATCH]
[ATTACK:MAIN:BYTYPE:GRASP:punch:punches:1:2:BLUDGEON][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:RUTC:slash:slashes:1:4:SLASH][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:LUTC:slice:slices:1:4:SLASH][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:RLTC:stab:stabs:1:3:PIERCE][ATTACKFLAG_WITH]
[ATTACK:MAIN:BYTOKEN:LLTC:strike:strikes:1:6:GORE][ATTACKFLAG_WITH]
[ALL_ACTIVE][NO_SLEEP]
[FAT:4]
[BIOME:ANY_DESERT]
[BUTCHERABLE_NONSTANDARD]
[STANDARD_FLESH]
[HOMEOTHERM:10067]
[LAYERING:300]
[SWIMS_INNATE][SWIM_SPEED:2500]
The mountain/chasm one can fly and has extra damblock, the freezing biome one throws fireballs and can swim, and the desert/badland one has extra size and speed.
It's a bit hard to describe what the Flayls look like, but I imagine them as being large, strong, hairless humanoids, with a circular mouth (a bit like a lamprey, I guess?), four tentacles on the midbody, and fleshy predator-dreadlock-like things protruding from their heads...
Also, the body file:
[BODY:FLAYL]
[BP:UB:upper body][UPPERBODY]
[BP:LB:lower body][CON:UB][LOWERBODY]
[BP:HD:head][CON:UB][HEAD]
[BP:RUA:right upper arm][CON:UB][LIMB][RIGHT]
[BP:LUA:left upper arm][CON:UB][LIMB][LEFT]
[BP:RLA:right lower arm][CON:RUA][LIMB][RIGHT]
[BP:LLA:left lower arm][CON:LUA][LIMB][LEFT]
[BP:RH:right hand][CON:RLA][GRASP][RIGHT]
[BP:LH:left hand][CON:LLA][GRASP][LEFT]
[BP:RUL:right upper leg][CON:LB][LIMB][RIGHT]
[BP:LUL:left upper leg][CON:LB][LIMB][LEFT]
[BP:RLL:right lower leg][CON:RUL][LIMB][RIGHT]
[BP:LLL:left lower leg][CON:LUL][LIMB][LEFT]
[BP:RF:right foot][CON:RLL][STANCE][RIGHT]
[BP:LF:left foot][CON:LLL][STANCE][LEFT]
[BP:RUT:right upper tentacle][CON:UB][LIMB][RIGHT]
[BP:LUT:left upper tentacle][CON:UB][LIMB][LEFT]
[BP:RUTC:right upper claw][CON:RUT][RIGHT]
[BP:LUTC:left upper claw][CON:LUT][LEFT]
[BP:RLT:right lower tentacle][CON:UB][LIMB][RIGHT]
[BP:LLT:left lower tentacle][CON:UB][LIMB][LEFT]
[BP:RLTC:right lower claw][CON:RLT][RIGHT]
[BP:LLTC:left lower claw][CON:LLT][LEFT]
I haven't played that mod since I added these guys (a month or two ago), so I don't know how well they work out...