First Boone was gay, then that was retconned as he fell for Zayday. In his litany of all the things he's had to do, he lists "pretended to be gay", and then it's never been mentioned again except as a punchline. WHY was pretending to be gay important in the first place? And it's not even like he was out as pretend gay, he was playing a whole Victor Victoria thing: straight, pretending to be gay, pretending to be straight. None of the characters have asked about this flip flop despite the fact that he was posthumously outed, and then re-humously de-outed when he courted Zayday. So either he had to be convincingly closeted to convince someone specific, about his "secret," or it was somehow important to the plot that he WOULD be outed posthumously. To help get his death ruled a suicide? That seems incredibly flimsy. Again, no overt mentions of it to forward the plot. The only thing I can come up with is if he did it to help entice someone else to the red devil cause...and the only candidate for that seems to be Pete.
But here I get stuck in a catch-22: is Pete so desperate to get out of sex with Grace that he makes a false confession? But if the confession is false because he's gay then he WAS in on it with Boone and the confession is true. And who is he on the phone with in the last episode if Boone is really dead this time? I haven't got all of my thoughts on this properly organized yet. Both Red Devils have always appeared to me as too tall to be any of the Chanels - note particularly that when the three coconspirators take on Dean Munsch, Gigi is noticeably shorter than both of them. This fits the theory that both of Gigi's Devils are men. But if Gigi is working with Boone and Pete why would she refer to Boone as "your brother" to Pete? There has to be a third devil who isn't part of the "master" plot. But is he completely rogue or in cahoots with part of the main triad? Could Boone and a sister have recruited Pete (with Boone including romantic interest as part of his pitch), already planning to double cross Gigi? If so who is talking to whom really at which point? Which two Devils are acting when? And is Gigi (or Boone) always talking to the person they think they are behind the mask? Or was Pete acting completely independently from the triad, in cahoots with someone ELSE to use the mask of the serial killer to satisfy a different agenda?
Right now I think most likely Grace is the other devil (under Gigi) but NOT the bathtub baby. How much she actually knew going in and what she finds out when I don't know. I think she really wanted to change Kappa and was strung along by Gigi and/or Boone to believe killing would force the others to change their priorities for the better, the end justifying the means. Every time she makes one of her speeches to try and rally the sisters together and change things - and is blown off - it's a precursor to another murder. She underestimated how obstinate the kappas would be and it spiraled out of control. That's what her crisis of faith to Zayday before the slumber party was really about. Her quest for the truth is real and the promise of more answers is what's keeping her going.
Chanel could be the twin and not know it. Maybe a part of what Boone wants revenge for is that his sister was adopted while he was stuck growing up in an asylum? Maybe adopted into a ridiculously privileged life? Finding out she and Grace are REAL sisters could be a climactic endgame for the whole sisterhood theme. Incidentally, when describing her childhood Chanel says "then I came along" or something to that effect; she doesn't use the word born.
(Alternately, Melanie Dorkus was horribly disfigured by acid, it's never stated that she died. She was noticeably taller than the other girls and would have a valid reason for wanting to stay behind a mask, even alone with Gigi. Though I think it's extremely unlikely.)
I'm throwing all of this out there as an invitation to play with my loose puzzle pieces and maybe match some up! I'm not sure Pete's confession is going to turn out to be as meaningful as it was set up to look (i.e. He turned on the fryer to set up Kappa for a fall but that's ALL he did - he and Grace were at the coffee shop to hear the plan, explains why he's waiting in the bushes to see what happens).
I think the TRUE reveal is going to come down to what Dean Munsch said about cover ups: mysteries like this only work if every character only knows a little piece of the truth. And so I'm halfway expecting an ending like Clue, where EVERYBODY is the murderer at one point or another.