The buff to Extra Arms has been a huge improvement for use with Dragon Soul and general Combo Priest.  With Radiant Elemental you can do some pretty crazy stuff with them like this...

This isn't your typical combo priest though, making use of a few unusual cards like Dragon Soul, Arcane Giant, and Grave Horror for producing huge bodies at little extra cost.

Shadow Visions, Banana Buffoon, and now Extra Arms all give us cheap two-for-one spells which make Dragon Soul really easy to trigger and makes our giants cheap really fast.

Your hand can run out of cards really quickly if you're not careful though, so I've included a lot of cycle cards; Northshire Cleric, Power Word: Shield, Acolyte of Pain, Gadgetzan Auctioneer, and Lyra the Sunshard.

Since we don't run all of the health buffs that the usual combo priest would, I've also opted to include Mind Blast as it can provide the added burst needed to finish off the game after a Divine Spirit + Topsy Turvy play.

I chose Topsy Turvy over Inner Fire because it costs less mana, making Dragon Soul turns easier, and I find it to be all around more flexible.

I've been having an absolute blast with this deck and I do not regret crafting Dragon Soul and Lyra the Sunshard at all after playing with it.

Update:  I've removed the Gadgetzan Auctioneer for a Test Subject.  At 6 mana, the Auctioneer was really too slow for this deck and didn't get a lot done even with a Radiant Elemental on the board.  Test Subject lets us dump our buffs onto it with the assurance that we'll get them back barring a Silence or Transform effect on it, which is great for Dragon Soul synergy and it gives us even more arms!

Update2:  Replaced 1 Mind Blast with Eydis Darkbane.  With all the cheap buffs in the deck, Eydis can be another way to pop off without Dragon Soul or Lyra the Sunshard.  If the opponent doesn't have any minions up every buff cast on Eydis Darkbane is a free Darkbomb straight to the dome!