At the beginning of your upkeep, reveal the top card of your library, if it's a creature card that shares a creature type with a creature you control, you can cast this card without paying its mana cost. Otherwise, put it at the bottom of your library.
So now they're next leveling the Miracle mechanic and letting you cast your creature spells for free? (a.k.a. Miracle cost of zero.) It's only 3 mana to cast, it's a global enchantment (unlike Call to the Kindred), and it basically goes into any tribal deck that has access to green mana, right? This is mostly for casual but... it feels like it's just a Brainstorm or two away from constructed playable (if Brainstorm was legal in Block or Standard).
Nest Invader + Emerakul, go? I suppose it's too clunky for any serious constructed play, but the Avacyn Restored spoilers are just getting started and that makes you wonder... with the introduction of the Miracle mechanic, the existence of Delver of Secrets, and now that same idea bleeding into even more cards, there has got to be some library manipulation just waiting to be spoiled in AVR, right? What a strange set. The inclusion of a Brainstorm type card would make all of these cards unbelievably powerful and yet the absence of Brainstorm just makes you feel incredibly unlucky every time it doesn't work. An odd design.
--But enough of that. Let's talk about Cube.
Do you have a tribal Cube? I guess it's time to all this card to the list, because it's coming in. The only thing I had is that after looking through the oracle text for the majority of my creatures when building my Cube, half of the creatures have received creature type erratas since their original printing. It's like I need a cheat sheet to carry with me just to keep track of which card is what these days.