Well, we know that the original Claudio was the Builder of Dreams. We know he was capable of building dream gardens for people and that all his shamanry was related to dreaming - he wasn’t interested in anything else.
We know he broke while leading people through the spirit realm (which must therefore have some connection to his dream garden magic, else he wouldn’t have bothered with it), when he found the Titan Hyperiodax. We know that he was trying everything he could to anchor himself in the face of a…a presence so massive and overwhelming. We know that in desperation he even tethered himself to that presence to try and ground himself in some way.
So he broke while trying to forge connections and anchor himself.
Then you have his little spiel:
“The ability of an Aberrant—often called its anomalous effect—is always based somehow on the magic it was casting when it broke, with some variation and nuance. But there should only be one ability, even if it is versatile or has several facets. I cannot actually build gardens of hope and dream-stuff like my predecessor, but I am still capable of creating cruder concept spaces within the spirit realm. I can still connect people to the spirit realm with a binding of power—tethering them to it with an intense and unnatural directness. My ability here is a cudgel where my predecessor wielded a scalpel, but I have learned that if the emotions are strong enough, and positive enough, people are just as happy. For those who did not experience my predecessor’s magic, they cannot seem to tell the difference. This is an unusual and versatile bit of magic, and incredibly valuable in the hands of an Aberrant lucid enough to direct it, but it still conceptually fits together.”
Claudio moved to sit in front of Siobhan again, crossing his legs and leaving his back facing Mom’s frame. “The mental barrier in dreams is quite porous, which allows me to create this binding. I think of it like a tether, from myself to them, and from them to the place I choose. The longer someone is bound to a place or construct in the spirit realm, the more their mental barrier wears thin, and the other end of the tether will begin to affect them…viscerally. They act as both beacons and anchors for me, and I have found that, through very precise guidance, some of the nature—the idea—of the place they are tethered to flows back through them, to me. In this way, I can create new concepts for myself. Do you understand what that means?”
Siobhan had no real understanding of the topic, but he had seeded enough hints into his rambling monologue for her to guess. “You’re able to use more than your one, single anomalous effect?”
So, basically, if I’ve parsed this correctly - he anchors himself to others by tethering them to places in the spirit realm and then using the concepts that leak back through them when the barriers in their minds grow thin.
If you turn it on its head a bit, tethering might be his real ability - he’s tethered in an odd way to his original self and thus can cast the dream spell which in itself is a kind of tethering (but crudely). He tethered himself to Hyperiodax which is why he can walk in the spirit realm (but presumably less skilfully that the original?). He’s trying to gain more power, or rather, more powers by finding more ways to tether himself more strongly or to more beings, in an attempt to recreate what’s happened between himself and the echo of the corpse of Hyperiodax (if this is the power of just the spiritual echo…what happened in the mortal realm? Is this the source of the Black Waste? Is there another area blighted and twisted near his corpse? Or does it lie empty, his power contained entirely in the spirit realm?).
It makes me wonder about the connection between him and Siobhan in the current (future?) time. After all, when he attacked Lacer, did he use spells? I might have to reread that fight, but if he did, is he, in a way, tethered to Siobhan?! Gaining her abilities and using her to continue his life, such as it is.