Why Raviel and Fabled?
I just wanted to use them together. Demon angels cool
Does it work?
To a degree, yes. Fabled lacks a powerful boss monster, which Raviel (kinda) provides. Each archtype has several cards that have discard related effects, and so they can be used in tandem with each other to prepare for specific setups. Outside of discarding and graveyard related effects, you're essentially playing two different games at once. Fabled is going to shoot for synchros while your Sacred Beast monsters are going to try to bring Raviel out. Depending on the hand you may only go for one first, and then potentially draw into the next one later. Fallen Paradise combined with Fabled Ragin means that your always going to be able to draw two more cards regardless of where you start. Shooting for negates is really what Fabled is going to be aiming for here. Herald, F.A. Dragster, and maybe even Baronne are your eventual targets. Herald in particular can be easy seeing how you'll often have a leftover level 2 monster in Dark Beckoning Beast.
What About That Extra Deck?
Herald and F.A. for easy negates, linkuriboh for the occasional leftover level 1 monster, Brionac for non-destruction card removal (and discards), Chaos Ruler, and Baronne for some more boss monsters. Fabled Andwraith can force your opponent to dump a monster (if they don't read or if they only have monsters left in their hand), at worst acting as fodder for Raviel to get an attack boost, as best causing a discard on your way to a level 8 synchro. T.G. Hyper Liberian is there on the possiblity that you could get off tons of synchros, but it's honestly rarely feasible. I put cupid pitch at 2 precicely cuz it can be so hard to get to the higher level synchros, especially when you haven't yet gotten a huge card advantage. Levithan is just there to collect space tbh. Cool looking card, that's pretty much it.
What about that side deck?
Not a serious side deck, but some extra cards that seemed fun in theory but didn't make the cut due to consistency issues.
Anything else I should know?
The numbers on some cards isn't totally set in stone yet. I'm not super excited to have Raviel at 3 (two copies in a starting hand is a nightmare) but having him in your initial hand can save you a lot of headaches. Ash was originally at 3 but it can cause some issues when your trying to deplete your hand for Fabled Ragin. You can't really run any hand traps at all in this deck because of that.