Monstrous humanoid, usually NE, I guess. The main interesting thing is the mental link, which I guess allows them to flank. I'd also give them the "if one of a pair is not flat-footed, neither is" ability. What do you think about all that?
Before getting too far, it's worth mentioning that the D&D stats leave out a lot of the details from the original story I think are relevant.
Here's the story description from Fritz Leiber’s Lankhmar
(1996), which covers all the relevant points:
The Bleak Shore
[Swords Against Death]
Fafhrd and the Gray Mouser are sent to seek their doom by a small, pale, mysterious man. Unable to resist his curse, the two sail off in Fafhrd’s sloop as if in a trance . The sloop is crewed by four Mingol sailors indebted to serve it for life after being saved by the Twain from the City of Black Idols during their earlier travels. After a dream-like voyage of over 40 days, the small vessel reaches land, and the Twain send their Mingols back to Lankhmar. (Only one, Ourph, survives the journey.)
On the rocky island that is the Bleak Shore, Fafhrd and the Mouser discover two score giant eggs. Terrible gladiator lizards hatch from two eggs and, with talons as long and sharp as swords, attack the heroes. It truly seems the two have met their doom when the Gray Mouser finds and smashes an egg containing the embryonic form of the pale man, “lying here and sending its spirit abroad, lying here and calling men to doom.” The Mouser stabs this form with his blade. Instantly, the two snap out of their stupor, the lizards fall dead, the eggs crumble to dust, and the curse is broken—leaving the two heroes stranded “on Nehwon’s western continent, or on the easternmost shore of its eastern continent. No one knows.” They spend the next three stories trying to get home.
So it appears Gladiator Lizards are only part of a magical gestalt lifeform based on this "Pale Man" which somehow creates a cluster of "eggs" that contain Gladiator Lizards, then mentally projects to geas
creatures to come to its nest where the Lizards hatch to kill the victims, then the lizards eat them and somehow share the food between all the eggs?
The Bleak Shore, as indicated by its name, is a completely lifeless and barren area, so maybe that's the only way these creatures can obtain food.
Also, I wonder whether the "eggs" aren't technically cocoons
, and the Lizards spin them around themselves after they finish with their meal before waiting for the next geased
victim. If the Bleak One had to hatch an eight foot tall murder lizard every time a humanoid is lured into reach, wouldn't it gain less food value from its victim than it spent creating the Lizard that kills and eats them?
Also, if the "astral food sharing" theory is correct, then Gladiator Lizards that are taken off the island and used as guards won't want to cocoon, since they're getting fed by their keepers as well as the flesh of whatever intruders enter the area they're guarding.