NOTE: Edited 27/08/23
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According to the bestiary in Divah's guide—a section I'd read plenty of times, so I'd always be prepared for chance encounters like this one—despite its large size and superb talent for murder, a mist troll wasn't a great hunter because they were said to be super lazy, preferring their meals stumble onto their lairs instead.
What sort of lairs? Mist trolls were considered field monsters—a classification of monsters that spawned or built their habitats outside of dungeons—and they preferred the highlands, volcanic wastes, and ice fields where mist tends to congregate. So, yes, I should've seen this oskilgetinn coming. Although, to be fair, there were a lot of monster types that liked to hide inside the mist.
There was a chance I could get past this monster encounter without having to fight if I could manage to skirt around the seemingly blind beast.