KALKOTH: Monster Conversion - Lone Wolf to D&D adjacent and Call of Cthulhu 5e.

Kalkoth by Rich Longmore.

One of my favourite Lone Wolf monsters, from one of my favourite (and my first) Lone Wolf gamebooks - The Caverns of Kalte.

These big cats with paralytic venom dwell in the tunnels and chambers of Ikaya, a fortress built by the Ancients. There is a bit of At the Mountains of Madness flavour to the set-up, as the Ancients are long gone and -even though claimed as a palace by the ruler of the Ice Barbarians- Ikaya is basically a big dungeon, crawling with ancient monsters (including the shoggothesque Akraa’neonor) and leftover unstable magic. 

I think the Kalkoth would make a decent non-canon CoC monster, because of  association with some of those Lovecraftian themes. I've based the stats on the Panther (common to both RQIII and BECMI), though the CoC version is of more than animal intelligence. I don't know how I'd convert directly from the original gamebook system.

For Call of Cthulhu 5e... 

Kalkoth, Venomous Predators of the Snow-bound Ruins. 

A shaggy feline predator with a barbed, venomous tongue, Kalkoths are an artificial species that has survived and thrived. They’re mundane cryptids of conventional matter; their DNA is decipherable, but unlike any known living mammal species.

Their venom is effective against Mythos entities native to Earth and of conventional matter, such as Deep Ones, Ghouls and Serpent People. 

They have a particular animosity towards Mi-Go, going into a violent frenzy if they should scent one, suggesting that they may have been bred/created to guard against or even hunt down certain Mythos entities.

Kalkoths never hunt alone - there will always be at least two, working in concert. They are intelligent, but millennia without the conditioning of their creators means that they have lost what tool-culture they may have once had, beyond the use of doors and simple, pre-existing mechanisms (including traps).

It is rare that a Kalkoth will stray far from its home city, as they prefer the tunnels and sheltered streets to being in the open.

They are absolutely afraid of fire, and will retreat from a naked flame.

Unfamiliar with firearms, Kalkoths will only become afraid or wary of them through experience.

Their creator(s) seem more likely to have been from the Edgar Rice Burroughs end of the spectrum, rather than the Lovecraftian, and at least resembling humans (or Hyperboreans) - and are from thousands rather than millions of years in the past.

STR 3d6+6 (16.5)     CON 3d6 (10.5)     SIZ 2d6+8 (15)     INT 2d6 (7)     POW 3d6 (10.5)

DEX 2d6+6 (13)

Hit Points 12-13       Damage Bonus +d4    Move 9 (unimpeded by snow)

Weapons: 

• Bite 30%, d8 plus Tongue Barb attack
• Tongue Barb 100%, injects a paralytic poison of POT equal to the Kalkoth's SIZ. Subject is paralysed and oblivious for d3 hours, recovering with no memory of the attack
• Fore Claw 50%, d6 and if both hit, the Kalkoth can make an automatic Bite attack until the subject breaks free or is released (STR vs. STR)

Armour: 3 points of thick fur (0 vs. firearms)

Skills: Jump 40%, Climb 80%, Track by Smell 40%, Organised Hunt 25%, Sneak 45% (65% in snow)

Spells: None.

Habitat: The abandoned, snow-choked cities of their creators - inside the Arctic Circle, Antarctica, and in mountain ranges of the Americas and Asia.

Sanity loss: None.

...and for Old School D&D Adjacent

Armour Class +5     Hit Dice 4     Move 115% Normal Human      Morale 8

• Claw/claw/bite for 1-4/1-4/1-8 + paralysis (as above).
• Surprise 1-3 on d6.
• In the snow and ruins, surprised only on a 1.
• Must make Morale Checks every round if confronted with fire.