Like every beast to roam the halls of Grimrock, the Shrakk Torr started out as a normal fly, riding in on adventurers, then growing fat and laying their maggots in their corpses. The magic pulsating from the halls made them grow and change until they became giant things, scavengers of the dead and carriers of filth and disease. But so far deep in Grimrock, the bones have been picked clean... And these iridescent flies are tired of waiting for a new corpse to feed on. So nowadays, they make their own...
Giant flies deep in Mount Grimrock, Shrakk Torr are not very deadly on their own, but are still dangerous enough to be cause for concern. Their extremely fast flying and tenacious bites can disorient even seasoned adventurers, as can the sickness those bites often cause.