|Colors||Dark Blue, Golden Brown, White|
The Frostelus were somewhere between Rahi and Matoran; Frostelus may be former victims of the Visorak or some previously undiscovered species. How they came to be so near Metru Nui, and what their intentions may be, is unknown.
Norik and Iruini of Makuta Teridax's Toa Hagah ran into some on their travels, defeating them with a combo move in which Iruini's spear created a cyclone with which Norik fills with lava from his own spear, creating a lava tornado.
The Frostelus are extremely protective of their territories; once, a group of Frostelus launched an attack on a nearby Toa fortress which was guarding the Makoki Stone. The attack eventually led to the deaths of all the Toa except for Lhikan.
- According to the BIONICLE: Dark Hunters guide, the Dark Hunters were hoping to gain an alliance with the Frostelus. "Subterranean" was being used to negotiate with them, on the grounds that "he is one of the few beings uglier than they are".
- In The Kingdom, the Frostelus lived with Ko-Matoran in the region that was once Ko-Wahi.