This deck simply begs for Athreos, God of Passage , and no less than 3 copies if you intend to go all crazy with sacrifice effects. You also have Underworld Connections to help you increase your devotion.
Get rid of Orzhov Charm and Gild and instead replace them with the far more superior Hero's Downfall . Sideboard instead Revoke Existence and Glare of Heresy to better handle indestructible creatures.
I don't see that much usage for Agent of the Fates so you can drop them. You don't have that many heroic triggers.
Replace Herald of Torment with the currently superior Desecration Demon .
I would also drop Silent Sentinel - its high mana cost makes it a poor choice.
If you can afford, replace the Sin Collector s with Thoughtseize for better hand control.
Treasury Thrull is also highly expensive for what he does.
Final point is to try and keep your mana curve under control. Crypt Ghast can indeed help get a lot of mana, but he's highly vulnerable to removal, and if you lose him you might end up with a hand filled with high cost bombs you find yourself incapable of playing.
Against aggro you can sideboard Drown in Sorrow and/or Bile Blight . They are both superb choices for handling masses of tiny creatures early game.