yavimaya wurm from urza's legacy
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Add in Cruel Ultimatum
Hymn to tourach is always good
consecrated sphinx + psychosis crawler + howling mine/font of mythos dishes out a lot of damage. And if you want megrim and/or lilliana's carress to work, you need to find cards that specifically say "discard" otherwise you don't do damage with the enchantments. Hymn to tourach is a pretty good mono black card that causes discarding. All in all, it seems to me that you have two deck ideas going into one deck, and i think that if you picked one, and stuck with it, or made two different decks, than you'd have a better end result that what you have going here.
underworld dreams with burning inquiry and wheel of fortune is always pretty nice too. kinda meh because of the 3 black casting cost, but if you get anything that causes them to draw and discard, it REALLY hurts. Food for thought.
check out my myr deck, and maybe you'll see something you'd like to try out. http://www.mtgvault.com/ViewDeck.aspx?DeckID=106914
I would consider putting mycoloth in. it works especially well with doubling season.