Now that my next plotline is about to start up and I'm building the main antagonists, I figure the easiest way to represent the powers of their sorcerers is to give them a special kind of Sponsored Magic. Also used for the few corrupt humans who they manage to get on their side:
Shonokin Magic [-4]
Description: The Shonokin are a most ancient race, predating human habitation of North America. In their heyday, they practiced great magic alongside technological might that humans are just now beginning to reach. When the Invaders came and wiped them out, they lost much of their power. However, they filled in the gaps by contracting with unsavory entities the world has largely forgotten.
Sponsor: Shonokin Magic is sponsored by the ancient race of Shonokin, and their dire masters from beyond. When choosing this though, specify whether your magic is sponsored by the "regenerationist" faction or the "annihilationist" faction of Shonokin.
Agenda: The Shonokin are primarily concerned with recovering their lost power. The two main factions have very different ideals on how to do this, though. Annihilationists believe in bringing down the wrath of their forgotten gods and wiping humankind (as well as their gods) off the face of the earth. Regenerationists believe in finding some way to restore their race's fertility, which is hampered by the fact there are no surviving Shonokin females. This may seem more noble, but they're willing to go to any ends to do this, including subjecting humans to horrific experiments. Also, they still believe in wiping out mankind, it's just a question of which should come first.
Evocation: Shonokin magic calls upon most ancient gods, but also technology long-lost. Regenerationists lean more towards odd technology, such as devices that warp and twist human bodies, while annihilationists lean more towards calling on the forgotten gods. Either way, the results are unnatural, alien, and disturbing.
Thaumaturgy: Regenerationist rituals often use technology, such as advanced lab equipment and humans rendered into stem cells (it is still magic though). Annihlationist rituals look more magical, but follow precise fractal designs.
Evothaum: Regenerationist magic allows the use of biomancy at evocation speed. Annihilationist magic allows the use of entropomancy at evocation speed.
Extra Benefits: Using either form of Shonokin magic allows you to interact with the actual Shonokin without penalty despite their alien nature. Also, your magic does not cause any problems with technology.
Drawbacks: If you are not a Shonokin, you gain their penalty to social interactions. People can just sense the otherworldliness surrounding you. (treat as "Dude, you're dead!" under the "Living Dead" power, without the additional effects of physical consequences)
Despite the fact I'm treating them as two different factions, they're actually not very different. It's merely a matter of priorities, and relations between the two are pretty cordial because there aren't enough left for any ideological conflict to be worth it.