As mentioned above, a few players figured out that Kalitas, Traitor of Ghet offers a similar level of disruption to the popular Rally the Ancestors decks, which won the last GP, as Anafenza, the Foremost. Having a decently sized creature with lifelink is desirable in a format with a pretty popular aggressive GR deck, making it a nice flexible card against some of the more popular decks. Of all the cards Kalitas, Traitor of Ghet saw the most distributed play, with a whole bunch of decks running 1-2 copies spread out between mainboard and sideboard.
Kozilek's Return was perhaps the most talked about mythic coming out of spoiler season. Pyroclasm has always been a popular and powerful card, so adding one mana for instant speed and free five damage board wipe when you cast your big Eldrazi is exciting to say the least. Kozilek's Return didn't have quite the penetration to live up to its hype, but more of the initial talk was directed at Modern. With the Pro-Tour looming on the horizon we'll see how it fairs in decks like GR Tron.
A few decks stumbled on Sylvan Advocate as a cheap early creature to put you on the board against the aggressive decks that also wasn't a miserable draw in the late game as a 4/5 vigilance. As an added and sometimes overlooked bonus, it provides a nice boost to any manlands or awakened lands you might have as well. Note that multiple Sylvan Advocate will buff your lands accordingly, but not each other. Unless explicitly stated to be every card named that, when a card refers to itself by name it only applies to that one.
OMG Guys! Green Ponder!?!
Our first week with Oath of Nissa makes it look more like another card that hasn't quite lived up to its initial hype. Only one of the Eldrazi ramp decks in the Top 16 was using it - despite it looking like they would be interested in the filtering, though it did look more at home in the Top 8 Abzan Blue list. It allowed the deck to shave the numbers on several cards, help the splash into Blue, and it could even fix the four color mana base into double white for Gideon, Ally of Zendikar.
Similar to the painlands, Crumbling Vestige was an almost free way for many decks to splash into colorless mana. It saw inclusion in decks trying to cast Reaver Drone all the way up to ramp decks wanting a few more coloress sources for Kozilek, the Great Distortion.
Colorless non-tribal Nameless Inversion. Most of the time it's just a removal spell, but every now and then you might push lethal with a four toughness creature.
It's no Bile Blight, but the extra -1/-1 is pretty crucial. You still can't cleanly answer Siege Rhino, or larger, without another card or a block, but there are a lot of 4/4s that enjoy dodging all the removal locked in at three. Anafenza, the Foremost, Kalitas, Traitor of Ghet, and Thought-Knot Seer just to name a few. The double black is a serious investment in a Standard format that's promoted a lot of three and four color decks, but it's a nice payoff.