Few things strike fear into the hearts of any Awakened mage than the Abyss. In Mage: the Awakening’s cosmology, the world was shattered by a cataclysm long before written history. The Abyss was the result of this event, a rift that divides this, the Fallen World, and the Supernal Realms. Magic is drawn down from the Supernal Realms and through this Abyss to the Fallen World.
If anything, the Abyss is the antithesis of sane and logical Reality as we know it. Trapped as Mages are now in the Fallen World, every act of magic runs the risk of ushering in a little bit of the Abyss with it. The Abyss poisons magic, so that should a spell go awry, the Abyss seeps into reality and takes one form or another.
The tricky part about these Intruders from the Abyss is the fact that they never usually manifest the same way twice. Each intrusion is unique, which make researching it and understanding how they work very difficult.
It’s hard for me to go into detail in terms of motivation since the Intruders are not exactly like any other kind of entity in reality. Perhaps if there’s something that unites them it would be the fact that they active seek out to erode reality in whatever shape or form they take. Some are overtly destructive, taking on forms that erase entire chunks of reality, while others are more subtle, corrupting the laws of nature around them.
Again talking about specific forms is pointless. The best way to think about the Intruders from the Abyss is to take an aspect of reality and screw it up. One of the best manifestations I’ve seen for the Abyss are Brain Spiders. Not to go into too much detail but the excessive use of Mind Magics may provide the tiny cracks in reality necessary for these things to creep into people’s minds.
Partially a bug, partially something else, these Spiders multiply and inhabit minds, seeking to spread themselves to other hosts by virtue of magic. Sure they’ll kill the host, but by then, hopefully they’d have migrated to other minds. Other Intruders may take the form of a particularly disruptive meme, a virluent disease, or even full blown entities that can take more direct methods of carving out a niche here in our reality.
Intruders are some of the creepiest things that Mages can end up fighting against because they’re often phenomena that exhibit no logical behavior. Unpredictable, mysterious and always dangerous, the Abyss strikes against Mages by being that which they cannot comprehend. If the Seers are an obsession over power, and the Banishers are power without control, the Abyss is the unknowable, the ultimate mystery and the darkness that lies in wait for those foolish enough to dig far too deep.
For more information on the Intruders, and a host of excellent and creepy examples, check out Intruders: Encounters with the Abyss.