Lambent

The Lambent are mutated Locusts who have been infected by Immulsion. A yellow liquid-based parasite used as a fuel source by the Human population of Sera, who had also waged a civil war against one another for it, the Locust horde are aware of it's true nature and avoid it out of fear of becoming it's Lambent hosts. The Lambent are so named for constant yellow glow from the immulsion in their bodies, and each Lambent typically explodes on death, possibly due to immulsion's volatility.

History
Since its discovery, Immulsion was found to be a potent fuel when refined. This substance proved so valuable, the Humans of Sera fought each other throughout the Pendulum Wars, each governing body intent on claiming it for themselves. Unbeknownst to them however, Immulsion was actually alive, a liquid parasitic lifeform. Several Humans employed in Immulsion refineries found themselves contracting a terminal illness known as Rustlung from exposure to Immulsion. In actuality, Rustlung was an early indication of becoming Lambent.

In the underground hollows, the Locust found entire reservoirs of Immulsion. Due to the Locust originating from medical experiments focused on curing Rustlung, they each already had traces of Immulsion inherent to their biology. As a result, exposure to Immulsion caused Locust to almost immediately become Lambent. War broke out between the Locust and Lambent, with the latter gradually gaining ground. Desperate for a solution, the Locust Queen Myrrah commissioned a Human scientist, Professor Adam Fenix, to create a solution to the Lambent. However, his work was constantly delayed by the Pendulum Wars, turning his focus on other inventions such as the Hammer of Dawn orbital laser. Unwilling to wait any longer, the Locust invaded the surface and went to war with Humanity for 15 years, intent on claiming the surface of Sera and leaving the Lambent behind underground.

Over the course of the war, some Lambent successfully reached the surface, primarily infected Wretches, and were mistaken by Human forces as allies to the Locust Horde. The truth was discovered near the end of the war, when the Coalition of Ordered Governments launched a full scale assault on Nexus, the Locust capital city. There, Delta Squad, led by Sergeant Marcus Fenix, witnessed the Locust and Lambent fighting throughout the city, realising they were not allies as they initially assumed. To contain the threat of both species, the COG decided to sacrifice the city of Jacinto, sinking it to allow the ocean to flood the hollows and drown the Locust and Lambent together. During this operation, a Brumak is infected with Lambency and horrifically mutates, destroying the COG's lightmass bomb in the process. Remembering the Lambent's tendency to explode upon death, Delta Squad fired the Hammer of Dawn on the Lambent Brumak, killing it and sinking the city with its detonation.

Although the Human-Locust war was effectively over, the sinking of Jacinto resulted in Immulsion spreading into Sera's oceans, causing a global Lambent pandemic. Humans and Locust alike were beset by hordes of Lambent, including new mutations of infected Locust and even Lambent Humans known as Formers. During this crisis, Marcus discovered that Adam, his father, was still alive and held in captivity on the island of Azura, where he finally completed his solution to the Lambent. During the battle of Azura between the Humans, Locust and Lambent, it is discovered that the Immulsion countermeasure is designed to release a pulse of radiation that would eradicate all Immulsion on Sera, wiping out the Lambent without harming Humans. However, Adam was unable to refine its affect to avoid killing the Locust as well. Despite this, the countermeasure is activated and every trace of Immulsion on Sera. The Locust survived, rendered dormant and set to gradually become the Swarm, while the Lambent were purged entirely.

Variants

 * Former: Although lambency primarily affects Locust, even Humans may turn Lambent through long term immulsion exposure. Despite their rarity, Formers travel in swarms and may overwhelm their prey in numbers. Disturbingly, the consciousness of the Human the Former once was may remain, as indicated by their cries for help as they attack.
 * Lambent Berserker: Locust berserkers turned Lambent, the Lambent Berserker's mutation has caused it to sprout three tentacles from it's back, and the ability to spread immulsion from it's body in liquid and gas form as it takes damage. However, it's mutation is flawed in that it's heart is fully exposed by it's ribcage opening when it attacks, providing a weak spot for it's enemies to exploit. When killed, the Lambent Berserker's death explosion appears similar to a miniature nuclear explosion and is extremely devastating to anything nearby.
 * Lambent Brumak: Only one Locust Brumak is confirmed to have been infected by immulsion. The Lambent Brumak's extreme mutations include a replacement head growing from it's original mouth, numerous tentacles and it's own flesh anchoring it where it stood, rendering it immobile. Requiring the orbital weapon, the hammer of dawn, to be killed, the Lambent Brumak's death explosion was powerful enough to destroy an entire city (although it was directly underneath said city at the time).
 * Lambent Drone: Locust drones infected with lambency, Lambent drones behave almost identically to their uninfected counterparts. However, they explode on death, making close quarters combat against them a significant risk.
 * Lambent Drudge: Lambent drones mutated further by their lambency, Drudges are more durable and aggressive than Lambent drones, presenting a complete disregard for their own survival. When fatally wounded, Drudges may either run as close to their enemy as possible before detonating, or mutating to acquire new abilities. These include replacing their lower body with a large stalk, providing elevation and the ability to spawn Polyps, replacing their arms with tentacles to throw immulsion globules or rip apart their enemy, or replace their head with a tentacle-like appendage granting the ability to spray a stream of immulsion at their target. If the Drudge is killed with this last mutation, the "headsnake" may survive independently from the body.
 * Lambent Gunker: Locust Boomers infected by immulsion, Gunkers are twice as large as they were before infection and extremely durable. Gunkers are capable of slinging massive chunks of immulsion at their enemies, while using an elongated tentacle to attack at mid - to - close range. Unlike other Lambent, Gunkers explode in body parts rather than all at once, the arms detonating before the head, followed by the rest of the body.
 * Lambent Leviathan: A Leviathan infected with Lambency, the leviathan is mutated with several tentacles and the constant production of Polyps. Only one Lambent Leviathan has been documented.
 * Lambent Polyp: Unlike other Lambent, Polyps are purely immulsion formed into a solid entity. Polyps appear similar to oversized crabs with black and luminescent-yellow rock-like skin. While extremely vulnerable to most offensive means, Polyps travel and attack in swarms and explode on death.
 * Lambent Stalk: Large tree-like organisms, Lambent Stalks rapidly sprout from underground and deploy Lambent from their pods. Destroying said pods will "kill" the stalk, preventing Lambent reinforcements from being deployed from them.
 * Lambent Wretch: Wretches infected with lambency, Lambent Wretches behave identically to Locust Wretches, with the addition of self-detonation on death. Somehow, the Locust general RAAM was able to control Lambent Wretches as part of his forces.