Removed the Grixis Grimblades in favor of Black Cat. The Grimblade has served only as a suicide blocker, and only when there was at least one other Grimblade (or Lich Lord of Unx) in play. Poor utility.
Black Cat, in addition to being cute, can be cast with only black mana on hand, and has a disconcerting side effect of punishing your opponent for killing it. -3 Grixis Grimblade, +3 Black Cat.
Geralf's Mindcrusher is a very effective game-ender due to it resisting most removal apart from exile. Furthermore, it mills a second time. A very underrated card, really, and when your opponent's reeling from getting his stuff countered or Doom Bladed, you can afford to wait till turn six. -1 Relentless Skaabs, +1 Geralf's Mindcrusher
Undead Alchemist has proven itself to be the centerpiece of this deck, because while Diregraf Captain and Death Baron beef up your undead dudes, the Alchemist can multiply them exponentially, and tends to provide you with chump blockers so that you're not open even after an alpha strike. +1 Undead Alchemist.
I've still yet to get that Havengul Lich, at which point I'll likely remove the Highborn Ghouls and run 4x Black Cat.
After playtesting, Call to the Grave has proven itself to be an extremely frustrating soft lock if my opponent is playing with few creatures, and can at least slow down steamroller offenses enough to get my undying guys out.
