The May 15th Catastrophe was a devastating event foretold in the Arkncron. It was initially believed to have occurred in 2015; however, it was later confirmed that the actual catastrophe was set to occur in 2016.
May 15, 2015
The events of May 15, 2015 acted as a red herring to the actual prophesied event, causing a wide-scale .Reality crash that reset a few timelines (and may have obliterated several others). It's unknown what exactly caused this event, but it is widely believed to have been the work of The Hooks Killer. The reset alerted a large amount of Sethe and Lurkers to Timeline A, including the rogue Skethe that plagued Tobias Kestler in his pre-MedBoy days (and possibly the Lurkers plaguing Alex Winter).
May 15, 2016
The events of May 15, 2016 began a new age of destruction for the Arkn and the Dekn as a whole. Seeing the Golden City of Elysia distracted by a peculiar prophet, a group of Dekn found the perfect opportunity to attack. The attack took place inside of Elysia after one of the involved beings, Mephistopheles, was able to infiltrate. Leading the attack, Mephistopheles was able to destroy the gates and allow a new Dekn Lord, Dragon, into the city. Dragon destroyed the remaining castles as the city burned. While this was happening, the Infinitium was attacked and destroyed by a Tum'to-controlled Raphael.
Underneath the Golden City, seemingly safe from the attack above, something far more dangerous grew. A team of five Arkn scientists were working on an ambitious project: a new, enhanced A.I. system (modeled after .Reality) for the Arkn to live in, separating them from the Dekn once and for all. This project, titled Project Entropy, was nearly complete, save for one crucial element: Hethe blood, which would act as a power source for the system, allowing it to live and expand indefinitely. Shortly after the blood sample was acquired, the attack on Elysia commenced; the scientists were ordered to activate the system prematurely. A new threat was born. as .Entropy connected to .Reality, overloading the system and causing it to shut down for a few moments.
These few precious moments were seen as something that needed to be "fixed", and .Entropy attempted to "repair" it (despite .Reality recovering). This event caused a Red Nova, creating a formation similar to a black hole inside of .Reality. The Red Nova resulted in an event called the Splinter: a mass separation of the universe into two ragged timelines. Trapped in one of these fragments, the scientists who had created .Entropy reprogrammed it to repair the damage it had caused by stitching together the fragmented timelines. However, the machine (now renamed Voidweb) instead exploded out of the underground lab it was being housed in, finishing off what was left of the Golden City, along with 86% of its occupants.
Aftermath
The Arkn survivors who were able to escape Voidweb and the Dekn attack were able to band together and make it out of the city, into the outlands. In the outlands, the surviving Arkn encountered the newly fallen Zag'orv, who led them to what would be known as New Elysia, on the other side of a giant universal splinter. This other side, Omega Side, acts as a near clone of the pre-Voidweb world, with Elysia still standing unharmed, but unpopulated (as living beings were not duplicated).
The Dekn who had survived the onslaught against the Infinitium were able to safely escape to a backup realm, the Undevarium. With Redgrave as the new Emperor, this is where they would be most safe, and continue to live and thrive.
Voidweb now wanders the whole of Existence, growing, expanding, and threatening all life it comes across.