They're certain weird enough to be Aberrations. The centipede-dragon bit is odd enough, but what about detaching their skulls from their spinal column! Surely that would kill a creature with a normal anatomy?
I'm leaning toward Aberration but I'm not that strongly attached to it.
Guess it's up to Shade to cast the deciding lot.
After some more consideration, I think I'll change my lot to Magical Beast.
My initial impression was of some kind of octopus-dragon-centipede chimera who can separate its head from its spinal cord, but upon closer reading it's basically a long dragon-headed lizard with lots of legs, a pair of tentacles and a stretchy neck.
That sounds like it looks a lot like a Behir - indeed they might be related to Behirs - so it could easily fall within the Magical Beast type.
After all, Displacer Cats are vertebrates with tentacles and they're not Aberrations!
So, shall we say Huge Magical Beast with immunity to cold? I don't think they have the Cold subtype, as they are not vulnerable to fire.
A Behir is a Huge Magical Beast and is 40 foot long, with 12 HD.
Tiricheks are 30 feet long but have 13 HD. Maybe they're shorter and wider but weigh the same, as an adaptation to the cold?
Shall we use a Behir's ability scores as a foundation?
AD&D Tiricheks have an AC 3 better than an AD&D Behir, but only 1 better than the equivalent AC of the SRD Behir. I'd give its natural armour bonus a +3 boost.
Tiricheks are also dumber than Behirs, being Semi-Intelligent.
So something like this:
Tirichek
Size/Type: Huge Magical Beast
Hit Dice: 13d10+65 (136 hp)
Initiative: +1
Speed: 30 ft. (6 squares), burrow 10 ft.
Armor Class: 23 (-2 size, +1 Dex, +14 natural), touch 9, flat-footed 22
Base Attack/Grapple: +13/+29
Attack: Bite +19 melee (3d8+8) or tentacle +19 melee (1d8+8)
Full Attack: Bite +19 melee (3d8+8) and 2 tentacles +14 melee (1d8+4)
Space/Reach: 15 ft./10 ft. (20 ft. with tentacle or neck-stretch)
Special Attacks: Neck-stretch
Special Qualities: Can't be tripped, darkvision 60 ft., immunity to cold, low-light vision, scent, [
blindsense or tremorsense with tentacles?]
Saves: Fort +13, Ref +9, Will +6
Abilities: Str 26, Dex 13, Con 21, Int 3, Wis 14, Cha 12
Skills: ?
Feats:
Alertness, Cleave, Power Attack, Track +1? [if we use Behir's feats]
Environment:
Any cold?
Organization: Solitary
Challenge Rating:
8? [more HD than a Behir but lacks its special attacks]
Treasure: None
Alignment: Usually chaotic evil?
Advancement:
14-? HD (Huge); ?-? HD (Gargantuan)
Level Adjustment: —