While previews are officially one week away we have some more official Amonkhet news today thanks to this article by Blake Rasmussen. There's a lot to digest so let's break it down piece by piece.
These are two new mechanics debuting in Amonkhet. The article above contains the exact language from Matt Tabak's mechanics article coming next week but we're going to provide a brief summary of both here.
Embalm is an ability found on creatures that can only be activated from the graveyard. By paying the Embalm cost and exiling the card you get a token that is a copy of the creature except it is White, has the additional creature type of Zombie, and has no mana cost. You can Embalm only when you could cast a Sorcery. All creatures with Embalm will have its own token.
Exert is an ability that appears on creatures. You make the decision whether or not to Exert the creature when you declare attackers. If you choose not to Exert the creature attacks as normal. If you do Exert, you get to use the Exert ability but the creature does not untap during your next untap step.
Embalm and Exert also play into a new feature in Amonkhet packs - Punch Cards. These perforated cards will help you track what cards have been Exerted, Embalmed, which ones have -1/-1 counters (a returning mechanic), and what permanents have Brick Counters.
Here's an image of the Game Day playmat. The Game Day promo also reveals the Cycling will be making a return. In addition to Game Day, there will be an Amonkhet Open House on April 15th. These events will feature Standard tournaments and learn to play sessions featuring Welcome Decks. You can find the decklists in the linked article.
Finally, according to Twitter, it seems that the Amonkhet Masterpieces will be revealed, at least in part tomorrow.
Hey, I got a preview for one of the Amonkhet's masterpieces. Tomorrow I will unveil it. Tune in! #MTGAKH— Willy Edel (@bazardebagda) March 27, 2017
Amonkhet masterpieces look _quite_ different. Got one to preview on stream tomorrow! 0_o— Caleb Durward (@CalebDMTG) March 27, 2017