Thanks for the heads up about the new cards; looks like there are going to be a lot of powerful options in this set, and possibly some new tribal archetypes emerging for humans, spirits, zombies, and/or werewolves. Many of the cards below have already been mentioned by others, but as a first impression, these look like some of the potential highlights for various formats to me:
Nodes of Power/PvE
[spoiler]Anguished Unmaking - The efficient support removal that mono-black and mono-white decks have desperately needed.
Archangel Avacyn/Avacyn, the Purifier - Everything this card does is amazing, and it looks undercosted by about 4-7 mana at first glance.
Descend Upon the Sinful - The cheapest guaranteed board wipe yet, and if that’s not enough, Avacyn can even be used on the same turn to prevent your creatures from dying if enemies with menace or unblockable are ever a problem (obviously this “combo” isn’t the most mana-efficient way to kill most creature lineups, but it’s still one more broken thing Avacyn can do to put its owner ahead on cards and tempo).
Together, these could push Gideon Z (who I tend to think has a slight edge over Ajani in most cases) to become one of the most powerful all-purpose planeswalkers alongside Koth and Kiora. He now has most of the tools to build a control deck along the lines of the blue Drowner of Hope/Crush of Tentacles decks that often wreak havoc in NoP already, with Alhammarret’s Archive or Tamiyo’s Journal filling in for Prism Array. Perhaps a sample list could look something like this:
Archangel Avacyn
Veteran Warleader
Reflector Mage/Kor Entanglers
Anguished Unmaking
Descend Upon the Sinful
Smite the Monstrous
Encircling Fissure
Alhammarret’s Archive/Tamiyo’s Journal
Shrine of the Forsaken Gods
Oath of Gideon/Lantern Scout/miscellaneous
This kind of deck (minus the Warleader/Ally engine) might also be ideally suited for Nahiri’s strengths, depending on how the mana gains and ability costs turn out, as white’s main weakness right now is probably the inability to draw extra cards as efficiently as blue, green, and black, and to answer the Drowner/Crush matchup with large sporadic bursts of damage without putting itself too far behind when the next board wipe or Exert Influence hits.[/spoiler]Quick Battle
[spoiler]Devil’s Playground - This reminds me a little of Flametongue Kavu from way back in paper MtG’s Invasion block, in the sense that neither of its functions are especially exciting individually, but by combining average removal and an average creature, the card becomes a very solid all-around option that’s likely to gain some kind of tempo, card, or mana advantage almost every time it’s played.
Inner Struggle and Uncaged Fury - These will be great easier-to-attain alternatives to Exquisite Firecraft and Ravaging Blaze for newer players who want to branch out quickly from Origins packs instead of chasing rares, and might even be strong enough to replace some of the default red spells in top-tier decks as well.
Goldnight Castigator - This looks amazing for QB in general, and tailor-made for Koth in particular; the drawback will be negligible in many games, and in the meantime it’s essentially an Akoum Firebird at half the cost, which makes it perfect for stacking on top of Mirrorpool with a single red match.
Every other color has some interesting new tools to work with too, but I tend to think red is and will remain the best color for churning out maximum wins/hour in most cases, even if Kiora and now one or more white planeswalkers might wind up having a slight edge in win rate at almost the same speed in the long run.[/spoiler]Miscellaneous
[spoiler]Behold the Beyond and Seasons Past - While each can simply be used for the base effects as (arguable) upgrades over Painful Truths and Animist’s Awakening respectively, they can also chain into other copies of themselves very efficiently in the right deck, so it’s possible that one or both could be part of the next Prism Array/pre-nerf Awakening engine waiting to happen.
Fevered Visions - This might not be strong enough to edge out Jori En for the same role in most red decks, but it could shine as a new kill condition alongside Thopter Spy Network for Tezzeret, as many of those decks already rely heavily on Sphinx’s Tutelage to establish and maintain a soft lock.
Harness the Storm - Depending on how the timing works, this could potentially generate long loops of spells like Devour in Flames or Exquisite Firecraft by returning one after the other is cast, generating a cascade in order to cast the returned spell, returning the original spell and generating another cascade, and so on, repeating the cycle several times each turn before the gem destruction eventually fails to produce additional mana. That said, it might ultimately prove to be too inconsistent to justify building a deck around, or alternatively the timing could turn out to work in such a way that the cycle will end each turn after only one loop.
Westvale Abbey/Ormendahl and Thing in the Ice/Awoken Horror - These look like a lot of fun, if not necessarily competitive; while the restrictions are strict enough that it doesn’t seem easy to trigger their transformations reliably, building elaborate combo decks to make the most out of awkward cards like these could lead to some great war stories if we ever get the option to issue private challenges, organize house rules tournaments, or something similar in the future.[/spoiler]All in all, this looks like a very interesting set, and could shake up the existing meta significantly once some of the mythics start to trickle into everyone’s collections; while in an ideal world I’d tend to prefer slightly less aggressive powercreep among top-tier cards (especially in terms of mana costs), many of the effects themselves are unique compared to what we’ve seen up to this point, so hopefully we’ll wind up with a lot of new variations and archetypes emerging in the weeks to come, to shake up the Kiora/Koth stranglehold once coalitions are released and begin to gather steam.