Frost Men are in the Tome of Horror Complete, I have a copy for pathfinder but I hear there is a version for swords and wizardry. They are a solitary group that look like humans with innate magical abilities. Also the Adlet is a group of humanoid wolves with magical powers to control and conjure ice. Their shamans for example bind ice elementals to their will. I've made attempts to convert them to BECMI though along with some other things.

I like that idea of the Garl mimicking proto frost giant culture.

I ran a small group into the Great Glacier where they encountered six large twisting spires in which was inhabited by six cultist who venerated the towers as extensions of a 'god'. The cultist were 'mutants' or beastmen, didnt go into much detail on them. The 'god' wasnt active but did cause psychic warping of a lot of natives and the players need to make saves against losing their minds.

Also got a copy of Realms of Crawling Chaos recently, using its psionic rules for psychic mutations in cultist.