very interesting edh deck, although im not sure why skithyrix is in there. i wouldnt use any infect creatures unless i was running an infect deck. some good cards that could go in there would be Hex, sorin lord of innistrad, sorin markov, earthquake.those are just some of many cards i would use. there are some great new cards in return to ravnica that would go great in that deck when the set came out. its a lot of gold cards again which i really like. dreadbore is a return to ravnica card that would work good too, easy way to get rid of a pesky planeswalker

Skithyrix is there for fun. It never hurts to have a little infect damage in colors that can produce it well. As for Hex Its got a ton of removal already not sure if it needs more. I personal Don't like Earthquake. The Sorins don't really go with the theme of the deck which is Angels, Demons, and Dragons. Not vampires. Dreadbore is now in there so check on the addition.