So, at the end of Deception, G gets disintegrated. Just before that , he shows that he's able to derive energy from consuming souls.
In Epiphany, every soul that disintegrates is because of M, and M claims she is nourished by their destruction. Did M tear apart G (she had just returned from banishment, and he was apparently just sloshing with excess energy)? Perhaps more intriguingly (and haphazardly), did M teach the energy vampires how to eat souls in the first place?
We think of M as not having turned to evil before being banished to the void, but maybe that was just a game attempt at reform, or another layer of deception. G said he was about 200 years old, and M's clothes indicate that she's been spirit guiding for longer than that, and her comments suggest that many hosts have wished to be rid of her in the past. Perhaps the soul-eaters were an early attempt to end her own existence, or make the Bestowers and their guides unnecessary (no more lost souls to shepard, they've all been eaten). It might even explain how G recognized the threshold of infinity, if Madeline had another brainwashable host when she was first teaching the soul-eaters their tricks.
Or maybe not. If M could figure out the energy-draining trick, perhaps someone else did too, and while no hellspawn have showed up since Legacy, it does seem to be a universe where you could literally make a deal with the devil.
Anyway. Food for thought.