Going into the Pro Tour, this was my back-up deck:
Gather the Pack Abzan
The concept is to take full advantage of the delve mechanic and the high quality cards of Abzan, ensuring that you play them as often and mana efficiently as possible. Gather the Pack puts five cards into your graveyard, and helps find Siege Rhino or Tasigur, the Golden Fang. This allows the deck to deploy the most mana-efficient threats and answers, since Murderous Cut and Tasigur, the Golden Fang both will usually cost 1 mana (plus delve). Additionally, a high portion of the time you will flip a Deathmist Raptor, which can later enter the battlefield for free—using a Den Protector to make that happen, and Den Protector also returns value in your graveyard to your hand.
Evolving Wilds in the mana base maximizes the number of cards hitting the graveyard, and makes sure that you get 2 basic lands quickly so that your battlelands will come into play untapped. The mana looks scary, but it is actually reliable. You are exchanging this for extra copies of Shambling Vent, but I found activating Vent occurs less often than you expect.
You have a lot of choices when building your board, and these numbers should be considered soft suggestions as the metagame shifts. After sideboarding, you can choose to emphasize the part of the deck you care about most and pick the right tools. It is a tuner’s sideboard rather than dictating in-out decisions, since so many decks vary in how they are built and how they sideboard.
Against control, you’ll want to reduce removal spells including Murderous Cut, and you have Treasure Cruise to replace it as the delve target. You also gain access to Torrent Elemental, which is a remarkably nasty continuous threat for them to deal with, and the usual copies of Duress and even an Evolutionary Leap.
A major theme of this build is being ready for RG Landfall—my respect for that deck is such that I thought that this level of reaction was necessary. Your goal is to play games always holding up a removal spell in case they go for their combo. I’m not playing Jace, Vryn’s Prodigy largely because I found that versions that did so were too vulnerable to Landfall. It is possible that with pure aggression on the downswing, you could play him. Against aggressive strategies, you can side in a full set of Languishes, Murderous Cuts, and other instant-speed removal, and be confident that you can ruin their day.
If you get into a midrange grind, Torrent Elemental is great for breaking through and accumulating advantage. If their creatures are big, go with spot removal. If they have small creatures, load up on Languishs.
One key point is always preserve the deck’s creature count for Gather the Pack. You don’t mind not double-hitting under spell mastery, since that usually does not matter, but missing hits on turn 2 is really bad. The main deck runs 21 creatures, which is comfortable even if you don’t count Deathmist Raptor. You are fine to cut a couple of creatures, but you want to avoid going below the high teens. If you do, Gather the Pack becomes increasingly risky and will also need to be cut—your sideboard is unlikely to allow you to do this elegantly, since then you also would want to reduce the amount of cards you’re delving.
I encourage others to try this build. It is remarkably good at doing what it sets out to do, and has a lot of room for customization if you want to go after a particular metagame.