During the COG's last stand against the Locust Horde at Jacinto, it became clear that the Locust intended to destroy humanity's last stronghold by sinking it. However, Marcus Fenix and Delta Squad came to the realisation that sinking Jacinto could also be an advantage. The Locust had not yet evacuated their home city Nexus and so Delta Squad worked to try and sink Jacinto before the Locust could relocate. Once Jacinto sunk, the Hollow would be flooded with seawater, submerging the Locust city.
Marcus Fenix and Dom Santiago delved into the Hollow once again and stole a Brumak from the Locust stronghold. They rode the beast into the expansive caverns beneath the Jacinto Plateau, using the Brumak's weapons to destroy the large columns that supported the city above. However, the caverns were filled with high quantities of Imulsion which the Brumak would have to wade through to reach the columns. Marcus and Dom caused a partial collapse of the cavern, creating an opening large enough for King Raven choppers to descend through and pick them up. The Imulsion soon took its effect on the Brumak and the creature mutated, transforming into an even larger, bulbous monstrosity with several tentacles ending in snapping mouths.
Aboard the King Raven, Marcus used the Hammer of Dawn target painter to target the Lambent Brumak. It took three strikes from the satellite laser to destroy the monster and the resulting explosion triggered the collapse of the final supports, causing Jacinto to collapse and seawater to flood into the Hollow. While this wiped out the majority of the Locust forces, some managed to survive and go into hiding. Worse still, the flooding of the Hollow caused the Imulsion to rise to sea level, accelerating the Lambent's eventual rise to Sera's surface.
A standard Brumak reaches a height of fifty feet, but the Lambent Brumak reached almost twice that. It lost the use of its legs as they seemed to melt and fuse into the rock, rendering the beast immobile. The creature sprouted numerous tentacular appendages, each one ending in a ferocious maw lined with many jagged fangs. Its hide was far too resilient to damage with conventional weapons, only the Hammer of Dawn was able to damage it. Like most Lambent, the Lambent Brumak exploded upon death. The sheer size of the creature ensured an equally massive explosion, one powerful enough to collapse the Jacinto Plateau.