Fuzzy is Eric.
This one seems just about undeniable by now. Hazel talks about Eric as though he's died, but she also talks about him in the present tense. She gets upset
when Fuzzy acts differently to Eric. She was right there when Fuzzy woke up without his memory, and when he says "I don't even know
you" she doesn't respond, "I'm Hazel", but rather says, "...I'm Hazel"
— that's a pretty telling ellipsis. It has now been established
that either she or the cat is able to wipe memories. Sin seems to have immediately understood
that Fuzzy was mind-wiped by his former colleagues back when he was in a team of three thieves. The only question left, really, is "Why?".
UPDATE: This WMG is confirmed
Carlyle is Sam...from the future.
Time travel has already been established as existing, even if we're yet to see it outside of the twenty-four-hour version. And Sam's character arc seems to be slowly turning him from a shiftless, clueless loser into a brave, thoughtful badass who has seen and done it all — one key moment of his development already had him talking in Carlyle's preachy "fortune cookie"
speech. Add in the fact that Carlyle has at times seemed kind of like a guardian angel for Sam and Fuzzy, showing up at crucial moments and keeping them on track, seeming to know more than he should about their problems; and the fact that Sam has had so much trouble meeting Carlyle or even seeing his face that it seems kind of deliberate (other people like Fuzzy and Lance claim to have met him, but possibly Sam has changed enough in appearance — and let's face it, he has — that he feels that they
won't realise it's him). And to top it all off, it may have been presaged by this strip
UPDATE: This WMG is confirmed by Rikk Esteban in his completely canonical
alternate ending to Book 2 (sadly only existing in print).
The Pit that the Committee guards is the prison of Brain's race.
The first Committee sealed a race of Eldritch Abominations in the Pit but missed one — Brain. Brain's ultimate goal is to free them.