This is my 1,000th post. Also, this is the last monster from the Illithiad that I had to convert, but there are many other illithid-related monsters left! The gohlbrorn is a smaller relative of the bulette. It is relatively smart, can communicate subsonically on their own language, and can spit rocks. A cool monster, I like it.
At first I wanted to omit this creature, because this is not a separate illithid species, but an unique being. I am not very good at reading AD&D statblocks, so I was mostly guided by the description. In its normal form, Lugribossk is an ulitharid with an ability to exude corrosive slime. In combat, it turns into a 30-foot-tall glowing giant with sharp claws, able to tear apart enemies both physically and mentally. Maybe, if Lugribossk is slain, Ilsensine will create a replacement - hence the racial template provided here.
The trapper is the relative of the lurker above. It creeps along the floor and grabs people the walk over it, instead of falling on victims from the ceiling. For some reason it lacks the various senses of its ceiling-dwelling cousin, but is resistant to cold and fire. Probably no less obnoxious than the lurker above.
One of those weird classic D&D monsters. An oversized cloaker/darkmantle that drops from the ceiling, engulfs and smothers the prey. A lone adventurer doesn't really have a chance unless he has specific countermeasures. Dragon Magazine #150 lists the lurker above and the trapper as related to mind flayers, but I did not manage to find any connection.
The mind flayers are present even in the Dragonlance setting, although with some differences. First, they are called the yaggol, also known as akitu-shai or crawling maws. Their array of abilities is slightly different, and they are split into two castes - elites and savages. Also, they live in the jungles, not underground.