Irnakk was known for being the embodiment for fear in the myth and could make its victims' worst nightmare come true.
Irnakk was a legendary creature thought up by the Skakdi leaders in order to frighten their troops and keep them obedient.
During the main event of the story, it was brought into reality by the Zone of Nightmares, one of the many chambers of the fortress leading to the Chamber of Life.
Irnakk later make his appearance when the Toa Inika entered into the Zone of Nightmares. It then appeared from the shadows and confronted the heroes. During the heated battle, Irnakk uses its Zamor Sphere Launcher and proceed to shoot the sphere at Jaller. Then, Jaller began to hallucinate his worst nightmare, which was that he was dying as the Matoran in the hands of Turahk. Upon realizing that Jaller could not fight in this condition, Hahli, Hewkii and Matoro dragged him out of harm's way as Kongu and Nuparu stay behind to fight against Irnakk. Matoro then used his Zamor Sphere Launcher filled with energized Protodermis to heal Jaller and snap him out of his hallucination.
At first Irnakk was winning when it overwhelmed the Toa of Air and the Toa of Earth with its overwhelming strength. However, Kongu and Nuparu got back up and together, they combined their powers to weaken it. Enraged, Irnakk then tried to used its power against the two, although Kongu and Nuparu manages to break free from its power of fear. Nuparu then weakened it with his Laser Drill and grabbed him as Kongu began to charge his Laser Crossbow and then finally fire the energy towards Irnakk as latter was finally defeated and it crumbled on the floor unconscious. The Toa Inika then continue their quest of getting the Mask of Life.