Those who have used the Pattern to travel deep into shadow know that eventually, as one travels far out from Amber, the shadows grow wild and strange, and eventually, reality practically disintegrates around the traveler, forcing them to hold the Pattern to mind in order to stay in control. And those who have ventured down the Black Road know that it leads to the end of shadow.
The place beyond where Pattern-walkers can safely travel is commonly known as Chaos. They speak of the Courts of Chaos beyond, and those who dwell there, but this is much like an Earth-dweller speaking of Hell and the Dukes of Hell.
When you think "Chaos" at this point in time, think "boogeymen".
Please note that the Merlin novels' depiction of Chaos is entirely non-canonical on our game. Nobody knows the slightest thing about a Logrus, the Serpent, any relationship between Oberon and Dworkin and Chaos, or anything of that sort. If you are thinking about things in a second-series framework, stop. Remember that our cosmology is distinctly different.