- Subspecies of jormungand sleeping in the deepest cavern of Costlemark Tower. Although biologically classified as a serpent, the bilröst has evolved in such a way over the millennia that it now bears almost no resemblance to its land-dwelling counterparts.
- Size: 135.79 ft. Weight: 125.38 t
Bilröst uses both physical and magical attacks. Bilröst is weak to one-handed swords, daggers and ice. Its magical attacks are fire-elemental and capable of inflicting Burnt and Overheated. It breathes fire up into the air above itself, and it will rain down all around it (can be avoided by being far enough away). It can imbue itself with fiery energy and eject a shockwave of fire from itself as the epicenter. It shoots out a flaming stream that travels a great distance. It whips out with its long tail and lunges to attack with its fangs. It can coil itself around Noctis, trapping him and tightening the grip (the player can free-warp away).
Using ice elemancy against Bilröst works well, especially potent with Quadcast, Quintcast or Maxicast. The player can also make some Blizzaga with the Healcast effect, as item use is prohibited in this Menace Dungeon. Ignis's Enhancement bestows the ice element to Noctis's physical attacks. Character-swapping to him lets the player use powerful frostbind daggers against Bilröst. Prompto's Piercer can debuff Bilröst.
Bilröst is likely the original spelling of Bifröst. Bifröst was a rainbow bridge in Norse mythology that connected the realm of the gods, Asgard, with the realm of the mortals, Midgard.