A few more changes since my last update:
I forgot to officially say this, but Karn, the Released went in the last free artifact/colorless spot as soon as he was spoiled. He actually isn’t super exciting to me- I’m not really looking for more planeswalkers in the cube- but he’s been good, of course.
Justin and I have been playing some MTGO beta, and realized in the process that Life’s Finale is a huge bomb. It’s probably the Wrath you’re most likely to concede to, and just feels very unfair. We’re trying it out in the place of Tombstalker, which is considered a cube staple, but has never been good for us at all. Maybe we run more reanimation than most- I’m not sure of the reason for this. It felt like everything had to go right to make him even a bit undercosted, but many black decks still don’t want the drawback.
Masticore is out of our cube for now (with no replacement). His ability just doesn’t do enough to justify the drawback in practice, and power creep in creatures has been really hard on him. Basically I felt that without a way to abuse or negate the discard (either through reanimation, Squee, or lots of card draw), he couldn’t compete with other four drops, which makes him pretty narrow in practice. Razormane has an easier time competing with other cards, and I personally like the free damage (and often the ability to attack when Masticore can’t) enough to keep him in instead.
Molten-Tail Masticore is in a totally different position, since hitting faces is rad, and is in no danger.
Finally, Squee is out in favor of Urabrask the Hidden. He has a splashy ability and has been so good in normal limited that we felt he was worth a try in the cube as well. It doesn’t hurt that red has approximately one other five-drop, either. Squee is a card that is really cool in theory, but didn’t come together with the right pieces often enough to earn the spot.