Scarab Egg introduces the opportunity for new synergies that this deck was lacking.
Scarab Egg -> Ratcatcher / Unwilling Sacrifice / coin + Hellfire / coin + Ravenous Pterrordax on turns 2/3 are all solid and give a solid backup plan to the preferred combos:
Devilsaur Egg -> Hellfire / Ravenous Pterrordax / coin + Carnivorous Cube .
Later in the game you can cube Doomguard s, Voidlords, and Mechanical Dragons.
Dark Pact , Lesser Amethyst Spellstone , and Zilliax give you good sustain.