The Unicorn is not Order, nor the Pattern.
The Serpent is not Chaos, nor the Logrus.
The Unicorn and Serpent predate the Devices by a long time. IMC, both devices were created by brilliant men as tools for dealing with a harsh environment. The Logrus was a success, which led to failure. The Pattern was a failure which was made to succeed.
In My Campaign, the Logrus was a device created to deal with the encroaching Abyss. It succeeded very well, and later proved to have combat and secondary uses that led to great power and great success in the various conquests of the Courts of Chaos. Which led to a rigid power structure that downplayed respect for the innovation and risks that had created the Logrus. Hundreds of thousands of years later, PatternFall is the Chaos failure of this tradition.
IMC, the Pattern is a Chaos design conceived as an even more radical tool to use upon shadow. Unfortunately, it destroyed the minds of the Chaosians trying to implement it. The concept designer, Dworkin of House Nemirab, suffered two separate mental breakdowns and lost several of his immediate family to Weapon Project Amber. The project concept was finally declared a failure and abandoned when Dworkin was not well enough to continue.
After a series of unfortunate events forced Dworkin to flee Chaos for his life, and after several dozen more attempts to implement Event Amber concepts which killed thousands and thousands of more people, Dworkin finally received assistance from a previously unknown Entity.
Dworkin was able to realize the magnitude of shadow influence he sought, but not in the manner he envisioned originally.
Once achieved, Event Amber actually swallowed a significant slice of infinite shadow and converted it to stable material, killing all life in that slice of infinity except for the sudden island in the sea of night at the center of the implosion.
This was not the result that Dworkin had foreseen and in guilt and frustration, Dworkin walked away from the Pattern.
Oberon hammered a defensible home out of that failure which proved so baffling and uncontrollable to Chaos.