Guarding The Underworld

So a few things I'm noting. 

1) You're pretty torn between whether you're aggro or mid-range.  Ideally you should be all in on one strategy or the other.  That means a lowered curve for aggro or less emphasis on lesser creatures for the mid-late game like Spike Jester.  It can be hard to figure out which route you're going with, but making that distinction will be important.  Either go with a rakdos mid-range/control build OR go all in aggro.  If you sit on the fence, it'll likely mess you up.

2) Pack Rat is fun and all, and it can definitely win the odd game here or there on its own; however, given the recent influx of Bile Blight into the fray, when combined with your lack of card draw, and I think it'll under-perform for you.

3) Some number of Hero's Downfall would probably be ideal.  Dreadbore does much the same for one less; BUT, there's an issue in the sense that it's multi-colored (can't hit Soldier of the Pantheon) and it's only sorcery speed (so things like Stormbreath Dragon will just totally mess you up).  Ideally I think you should have some number of both.

4) You have Anger of the Gods in the SB but it is totally opposite to what you want.  It would take out practically every creature in your build AND exiles things, making it a problem with Underworld Cerberus.  I can see where Drown in Sorrow would be more of what you're looking for, as would Bile Blight in some quantity in the SB to deal with opposing Pack Rats.

5) Why not go the full 4x Blood Crypt?  You have plenty of time to pick them up between now and gameday...

6) Sire of Insanity in the board?  He's good, like insanely good if you get him out and he sticks, but you're going to totally change from an aggro-ish build to that post boarding?  You would be better suited to have more Rakdos's Return(RR) in the board - keep in mind that if you cast RR you can redirect the damage to a PW AND they still have to discard... it's pretty good I hear.

7) I'm not sure Blood Scrivener really would be useful either...

So, is there promise, I think so.  But you really want to figure out which strategy you're going to run and move much closer to it.  It's quite alright to have some pieces in the SB to change gears a bit between games, after all, you needn't simply just yield to particular match-ups; however, if you're divided in G1, it will often work against you.

Given the revamped look, I would say to drop Underworld Cerberus (I want him to be good too... ) and add 3x Anger of the Gods as you REALLY want to cover your bases against most aggro and smaller decks.  Then you can probably pull some combination of Lightning Strike/Magma Jet to slide in Underworld Connections.  To be honest, I'd pull the Temple of Silence and Temple of Triumph for your normal basics as, well, you don't want to bog yourself down with too many etb tapped lands and you already have a fair amount of scry with the 4 Temple of Malice.  I'd also toy around with Stormbreath over Exava as it's far more likely to get through.