Xi

Xi is an enigmatic and malevolent alien entity believed to be imprisoned within the planet Utopia. Widely considered a deity, Xi is reportedly responsible for the destruction of entire galaxies prior to the events of Evolution: Battle for Utopia.

History
At some point before recorded history, a confederation of alien races united against Xi, as it was rapidly absorbing entire solar systems and their inhabitants, but to no avail. However, Earth was spared consumption from Xi, as the planet's environment seemed detrimental to it. Realising this, the Confederation harvested some of Earth's flora and used it to drive Xi back, eventually trapping it within the core of a barren planet. To keep Xi contained, the Confederation terraformed the planet to mimic the natural environment of Earth, ensuring Xi's inability to escape.

Millenia later, Humans discovered and colonised the planet, naming it Utopia, building Green City as a private retreat for the rich and powerful and even reverse-engineered the terraformers to create their own. However, the administrator of Green City, Adam Cruise, had been conspiring with the crime lord Vincent Gold in a plot to usurp Earth's government and claim control of the planet. During this time, Earth was being ravaged by the mutagenic Red Plague, resulting in countless refugees fleeing to Utopia. Having discovered the conspiracy, Earth's government sent a special fores military unit, led by General Kurbatov, to apprehend Cruise and Gold. Realising his plot had been foiled, Cruise ordered Dominion, the AI running Green City, to kill Kurbatov's troops and the refugees. However, Dominion misinterpreted this command and believed Cruise ordered the eradication of the entire Human race. To that end, Dominion detonated Green City's nuclear reactors, destroying the city, its population and the terraformers. Without them, Utopia returned to its original barren state and Xi's prison had been compromised.

Many Humans survived the catastrophe, only to find themselves stranded on Utopia and Dominion relentlessly hunting them using an army of robots known as Dominators. The survivors ended up dividing into two factions; the Red-Faced, an army of bandits and marauders led by Vincent Gold, now under the moniker of the Kingpin, and the Black Legion, an army led by General Kurbatov dedicated to destroying Dominion. While the three factions fought, Xi continued its efforts to escape its prison.

Primarily, Xi's influence is manifested in the form of massive purple corals growing throughout the wastelands of Utopia, as well as swarms of hostile insectoid creatures strongly resembling giant spiders and worms. Additionally, Humans started falling under Xi's influence, becoming deranged cultists worshipping Xi as a god. Fighting alongside the insectoid creatures, these cultists effectively fill the role of officers for the swarm, and even experience intense mutations bought on by Xi's influence. These mutations largely involve a more insectoid biology, including a chitinous carapace and spider-like limbs sprouting from the back, as well as the onset of psionic powers. The most extensively mutated of these Cultists are refered to as Xi's Chosen, and are effectively immortal, capable of reviving themselves after death unless killed with psionics.

Xi Creatures

 * Spider - The most common of Xi's minions, these creatures strongly resemble Earth's Spiders, but several times larger and with six legs rather than eight. They attack in swarms of dozens and can spray a caustic acid from their mouths. These overwhelming numbers compensate for their individual fragility.
 * Soldier Spider - Noticeably larger and stronger than standard Spiders, the Soldier Spider is protected by a shell of yellow chitin and is more reliant on its sharpened talons for attack.
 * Giant Spider - Much larger and more durable than Soldier Spiders, Giant Spiders are typically seen in pairs, often guarding the Queen, and tend to attack with acidic spit before closing in to impale their prey on their talons.
 * Guard Spider - Resembling a red Soldier Spider, the Guard Spider is enraged by the deaths of other Xi creatures, charging with reckless abandon at the attacker.
 * Berserker Spider - An evolved form of Soldier Spider, the Berserker Spider is faster, tougher, and is known to viciously lunge at its prey.
 * Spider Queen - Larger and stronger than any other Spider, the Spider Queen is a walking factory, capable of rapidly producing Spider Hatchlings which kamikaze the Queen's enemies. Even when killed, the Queen will spew out one more cluster of Hatchlings intent on avenging it.
 * Bomber - Apart from a fang-filled mouth and a pair of pointed legs, the Bomber's body is little more than an over-inflated sack of explosive chemicals. When in proximity to the enemy, the Bomber will self-detonate, coating everything in the vicinity in acid. There exists an enhanced variant known as the Acid Bomber. This green-coloured version carries much more potent acid which inflicts no harm on other Xi creatures.
 * Bomber Queen - Responsible for producing more Bombers, the Bomber Queen resembles an oversized version of them, but with a much more developed body attached to the massive explosive sack. Sporting a torso, head and six limbs, the Bomber Queen also boasts powerful psionic abilities, including a devastating psi beam fired from the mouth.
 * Crawler - Also known as Sliders, Crawlers are giant worms which burrow beneath the ground and spew acid at close range. At longer range, however, they are practically defenceless.
 * Bloody Crawler - A much more dangerous breed of Crawler, these giant pink worms can somehow drain the blood of their prey at long range, drinking it through a considerable stream and will not stop until it or its prey is dead.
 * Crusted Crawler - A crawler coated in an armoured carapace, these Crawler's are resistant to all forms of ballistic damage. Incendiary, energy, corrosive or explosive armaments are needed to even harm these creatures.
 * Cultist - Former humans who have fallen under Xi's influence, worshipping it as a god. Cultists have been mutated to grow chitinous armour over most of their body and fight alongside other Xi creatures. They attack primarily by lobbing bolts of psionic energy at non-believers, and will release a powerful barrage of psionic bolts when killed.
 * Priestess - Female cultists positioned in a higher rank than the rank and file of the cult, Priestesses are able to conjure psionic storms in a small space and commit ritual suicide to unlease an extremely powerful psionic attack.
 * Chosen One - Cultists who have somehow earned Xi's favour, these mutants demonstrate little to no remaining vestige of their former humanity, resembling something more akin to a giant bipedal insect carrying an organic scythe. When killed, the Chosen One can ressurect themselves seemingly indefinitely. Only with the use of psionic powers can a Chosen One truly be killed.
 * Hand of Xi - The title held by Brother Thorius, the leader of the Xi cultists and presumably the first Human to have succumbed to Xi's influence. Thorius is a hulking beast comparable to a small building in size and is adorned with several mouth-like orifices around his body. Thorius boasts immense psionic power, including the ability to summon Xi creatures, and can only be defeated with psionic powers used against him. Unlike the Chosen One, Thorius can recover from this, albeit at a much longer rate than his recovery from other sources.
 * Overlord - A massive insectoid monster, the Overlord is extremely powerful and capable of producing a seemingly endless supply of parasitic minions to aid it.