More singleton breaking here.
Here's the basic premise: I'm including 3 copies of Birthing Pod. Bye bye Survival (which has been less than stellar). Pod is a pretty unique card to build around, and is pretty much ideally suited for cube design. It's not mechanically isolated, all you need are creatures on a curve. It offers tons of creative drafting options, and doesn't force you to commit to the Birthing Pod line as your cards will have plenty of overlap with other archetypes. I think as far as cube combos go, engine cards like this are the way to go. As we've seen from Standard and Modern, there are all sorts of cute synergies and interactions you can pull with pod.
I know there will be some reservations about supporting an archetype so explicitly with multiples, but it's really not so different from using mechanically similar reanimation spells / burn spells / counterspells / whatever makes archetypes tick.
This is for random discussion and brainstorming of how these changes should affect a cube's design.
For one, I'm going to be adding Mikaeus, the Unhallowed, as a bit of an overlap between Pod and the Gravecrawler aggro idea. This card is a fairly outrageous pod top-end. Undying Acidic Slimes and random dorks are pretty ridiculous. Also, we open up some real combo possibilities that take set up: Mikaeus + Murderous Recap / Kitchen Finks and a sac outlet (Carrion Feeder, Greater Gargadon, Goblin Bombardment)
It also provides another archetype that can conceivably get Geralf's Messenger into play. I know the card is pretty narrow, but the pool of black three-drops is pretty awful all around.