It can spawn something like this
[CREATURE:BADVERM]
[NAME:badverm:badverms:badverm]
[TILE:249][COLOR:0:0:0]
[VERMIN_HATEABLE][VERMIN_ROTTER]
[FREQUENCY:1]
[BODY:UNIVERSAL]
[ATTACK:MAIN:BYTYPE:MOUTH:bite:bites:100:100:GORE][SPECIALATTACK_SUCK_BLOOD:100:1000]
[EXTRACT:concentrated darkness:1000:0:1]
[EXTRACT_ANTIDOTE:holy power:500:0:0:50]
[EXTRACT_FIXED_TEMP:10]
[EXTRACT_HEATDAM_POINT:10155]
[EXTRACT_IGNITE_POINT:8]
[EXTRACT_BOILING_POINT:9]
[EXTRACT_STUN_INTERMITTENT]
[EXTRACT_PARALYZE_INTERMITTENT]
[EXTRACT_PERMANENT]
[EXTRACT_SPEC_HEAT:50000]
[EXTRACT_SIZE:25][VERMIN_BITE:100:bitten:USE_EXTRACT]
[MATERIAL:STONE:OBSIDIAN]
[SPEED:100]
[FIREIMMUNE]
[HEATDAM_POINT:30020]
[BOILING_POINT:30000]
[MELTING_POINT:27000]
[FIXEDTEMP:25000]
[IGNITE_POINT:26000]
[COLDDAM_POINT:1000]
[CANOPENDOORS][MISCHIEVIOUS]
[POPULATION_NUMBER:1:5]
[BLOODTYPE:W]
[NOT_BUTCHERABLE]
[PREFSTRING:ability to disgust]
[PREFSTRING:ability to poison]
[ALL_ACTIVE]
[NO_SLEEP][NOSKIN]
[BIOME:GLACIER]
[trIGGERABLE_GROUP:5:50]
[CAN_LEARN][SLOW_LEARNER]
[MUNDANE]
Add [ITEMCORPSE:VERMIN:NO_SUBTYPE:BADVERM:NO_MATGLOSS]to your creature and see destuction of your fortress unless you have some heat-resistant cats. Fixed_temp and other stuff with temperature can be removed to make it not burning, but only venomous, very venomous.
A few critiques on that, if I may.
The attack might be useless as I don't believe vermin can attack.
Extracts' temperatures don't work (if at all). They won't cause anyone to burst into flame from being injected. Nor does antivenom work. I'd just remove the redundant tags.
[MATERIAL:STONE:OBSIDIAN] doesn't really do anything. You can't attack vermin anyway (everything that can oneshots them).
Vermin don't need body parts.
If it's fire immune, don't give it a heat dam point.
You can't touch it due to its heat, might as well just use the extract as a venom and leave out most of the redundant tags.
Opening doors, learning, being mischievous, are all designed for full sized creatures. I don't think it'd work well for a vermin.
[NOPAIN][EXTRAVISION][NOSTUN][SMALL_REMAINS] because it's a vermin with no eyes. This removes constant blacking out from pain (assuming vermin can even do that). It also adds the standard vermin corpse that only rots once.
[BLOODTYPE:W] doesn't matter when vermin are oneshot every time.
[BODY:UNIVERSAL], UNIVERSAL is not an actual body part. Vermin don't need bodies anyway.
Finally, this thing is definitely not [MUNDANE].