So I've got a work-in-progress Wrexial deck. It's all about milling the opponent & stealing their stuff. Haven't added in basic lands yet, but I'm guessing the mana base will probably be 38 - 40 cards. I'm trying to figure out what to put in to the 4-mana slot, since my curve is a little weird right now (there's a big gap at 4 mana). This is gonna be a casual deck, so no over expensive cards like Damnation or anything like that. What is this deck missing? Or what should I swap out?

http://deckbox.org/sets/428680