CORRUPTION & VOID

There is a single type of crystal called a Void Crystal, which was created in a lab, in an attempt to make the ultimate power source.

Though successful, it brought along destruction and a tear into another dimension, unleashing a plague of Corruption onto the planet. The Corruption can infect creatures, people and the environment in devastating ways that disrupt ecosystems. Currently, there is no 'cure' for this Corruption, but efforts are being made to push it back into the dimension it came from.

Lost and Wandering Spirits who cross through tears (Void Rifts) into the Living Realm get turned into Void Spirits. They were accidentally created with the discovery of Void Crystals. They are incredibly dangerous and cause mass destruction. Not only that, but they become carriers of a disease known as Corruption, which spreads to other Spirits as well as living flora and fauna, turning them hostile. Many military efforts have been unsuccessful in eradicating the Void Spirits, and no known cures to Corruption currently exist.

The Void and Corrupted take on the appearance of spectral beings, with flaming dark energy and aura. Glowing bodies that sparkle like the night sky and shift like a dense smoke.

Corruption has environmental impacts on the Living Realm which are not good. The Corrupted no longer play their role in their respective ecological niche, and it throws off the natural balance. Prey becomes predator, and predators become insatiable - this can include cannibalism. The growing number of predators and reducing prey, only adds to the unbalance. This also affects the habitats the creatures would normally be, the wilds becoming more untamed and plant life not being kept in check by herbivores. While other plant life may also become corrupted if exposed to too much of the infected creatures. Which then corrupted even more creatures, and so on. Eventually, habitats become inhospitable.

TLDR;

An ultimate power source was created, a Void Crystal. Upon its creation it exploded and opened a tear/rift into the Spirit Realm. Lost and angry spirits came through the tear/rift and are called Void Spirits.  These spirits carry a disease called Corruption, which can spread to all living things who are then called the Corrupted. Currently there is no cure for corruption, and efforts are also being made to hunt down the remaining Void Spirits. 

Void Crystals Creation Rift into Spirit Realm Void Spirits arrived Void Spirits spread Corruption Corruption continues to spread on its own Collapse of ecosystems & society.

Also: SPIRITS