So to begin your journey into Theros (and I suppose Nyx), we polled the pros to get their take on the top, most powerful, most defining cards of the format. Those that were mentioned the most -or the most emphatically – were placed higher on the list.
All of these cards were mentioned by someone—but only that one. Good enough to make people sit up and take notice, not good enough to warp the format around their little, or large, fingers (assuming they even have fingers).
In Standard, Ashiok is pretty much sitting on the sidelines. In Block Constructed, however, difficulty attacking Planeswalkers – especially ones as cheap as Ashiok – can give control and midrange players a leg up against decks that aren't aggressive. In those instances, it's really the threat of the ultimate softening them up in the long game, but when to players have Courser of Cruphixes staring at one another or are holding a handful of reactionary, non-Hero's Downfall spells, Ashiok can be a real nightmare.
For decks that are trying to go under the midrange and control decks, there's virtually no threat better than Brimaz, King of Oreskos. Cheap, hard hitting, and in a color that certainly doesn't mind having extra tokens sitting around, Brimaz is a key card in nearly every aggressive white deck, and even some of the slower ones.
It's hasty. It flies. Big and fast, Stormbreath Dragon is, along with Polukranos, World Eater, one of the prime threats in the R/G Monsters deck – just like in Standard. There's no twist, no special deck, no trickiness or shifty metagame calls. There's just face beatings and the match slip signing that usually comes swiftly once the dragon has taken a bite.
Xenagos, the Reveler might not be Elspeth, Sun's Champion, but then again, there are 563 cards in this block that have the unfortunate distinction of being "Not Elspeth." But for not being Elspeth, Xenagos still does a pretty bang-up job of being a difficult planeswalker nut to crack. Sometimes coming down as early as the third turn, Xenagos always gets in some value, even if that value is merely a 2/2 satyr. As Patrick Chapin said, this format can come down to "I play something, you deal with it, I play something else, you deal with it," so anything that can leave behind even a bit of value, whether through damage or creatures, can give a player a leg-up in any attrition-based match-up.
"It's probably the best finisher in Block."—Paulo Vitor Damo da Rosa
To anyone who has played with Prognostic Sphinx in Standard, that comment seems a little, well, odd. It just seems like there has to be something better to do than a 3/5 flier for five that can get occasional hexproof while providing some admittedly hot, hot scry action. But the Progfather has a lot going for it. It's one cheaper than Elsepth, so it comes down earlier and then dodges Elspeth's ability to wipe out four and more power creatures. It flies, so Elspeth tokens don't bother it. And it's big enough to take down the six-mana walker in two hits. It does all of that while matching up really well against the format's removal suite, a suite that doesn't include sweepers capable of downing the Prognostic Sphinx.
More than just a removal spell, Silence the Believers can destroy multiple creatures with strive, take care of troublesome bestow creatures with its extra exile clause, or, in the best cases, both. Expensive for removal, but this format is well tailored to suffer from a crisis of conscience when all of the believers are silenced.
"It's the best red card in the block."—Conley Woods
Woods has an occasional penchant for overstating things, but he's pretty spot on here. Prophetic Flamespeaker was touted highly by a number of pros and, alongside Stormbreath Dragon, is one of only two mono red cards to garner any mention. Considering Mono Red is an actual deck in the format, one that existed long before Flamespeaker began prophesizing, that speaks highly for this 1/3's power.
There's not much to say here. Hero's Downfall is important because it's the cheapest universal removal in the format. Important because it kills planeswalkers which, as this list can attest, are pretty important. Important because it slices, dices, and makes midrange and control viable.
Sylvan Caryatid and Courser of Kruphix are sort of a 2a and 2b on this list, though no one's really sure which is A and which is B. Not that it matters, as any deck playing one of them is almost certainly playing the other as well. Every pro we talked to who mentioned these two cards—which is also every pro we talked to—mentioned these two cards in concert. Caryatid makes difficult mana better, and Courser of Kruphix gives both life gain and card advantage to the plethora of midrange decks in the field. If a deck in the format is playing green cards, it's playing these two—and it's likely it's playing green because of these two.
Far and away, easily the most important and powerful card in the format. In fact, Elspeth looms over the format so much that several players nearly forgot to mention the six-mana planeswalker, taking it as a given that the Sun's Champion was the one you wanted by your side. And if you've been paying attention (and didn't just skip down to No. 1), most cards are measured against how they perform when Elspeth is around.
Elspeth serves as the level one test of the format: either you win before she matters or you contain her when she does. Or, you know, play your own.
Whether the best deck ends up being one that plays her or defeats her, there's no doubt that Elsepth, Sun's Champion, is the card to watch this weekend.