Fanwankin' Time
Prepare to witness the awesome explanatory power of the Grand Unified Theory of Cheetahs1!
Sebastian, through Circe, learns about Urzkartaga and the Cheetah, and also that Dr. Psycho is potentially powerful enough to mindfuck Hermes. He has Psycho send a mentalgram to Urzkartaga, and negotiates his deal. Cooperating in this plan is Urzkartaga's first real attempt to re-assert control over the Cheetah after Barbara has proven herself, in at least four different ways, to be unsatisfactory (from his perspective). These are
She was not a virgin prior to their marriage.
She has no faith in him, speaking and thinking of him as an object.
Her obsession with the Lasso of Truth, especially once she obtained it, bordered on infidelity, and kept him out of blood sacrifice for an extended period of time.
By the same token, her dealings with Circe amount to a conspiracy between Barbara and Circe to steal his power, and denying him the blood sacrifice that he'd been missing since the lasso fiasco.
Urzkartaga tolerated these for Chuma's sake, and because Barbara suffered for each of them; either by his will or natural consequences (also, he must've been famished for blood when Barbara finally got out from under Circe's thumb). However, when Sebastian brings these things up together with his first wife's failure, which led to the destruction of his tribe (not necessarily or even reasonably her fault, but you could spin it that way) and Circe's role in trying to steal his power, it's not far-fetched to believe that Urzkartaga could see something in Sebastian's "women suck" theory.
Of course, Circe (from this point on Urzkartaga must really hate her) shows up and Sebastian starts banging her, so the bloom probably comes off the rose PDQ. Even so, Sebastian seems to bring a reverent attitude to the ritual, even if he doesn't know it quite perfectly. He never treats Urzkartaga like an object and he's a steady supply of blood sacrifice.
Psycho hangs on as a medium and IIRC a part of the Silver Swan project. Or was he only there for the first Swan? Anyway, the fight with Donna is a smokescreen for Psycho to pull the real Urzkartaga off-stage so they doesn't get smashed. How much of the dialogue is channelling genuine Urzkartaga or Psycho bullshitting Donna, YMMV. When Angle-man tries to use his power on Urzkartaga, Psycho becomes disoriented (having space and time flip out on you can do that) and can't retain his focus. (Also: Psycho's oughta-be-famous-crazy-eyes2 make an appearance!).