As posted in The Rumor Mill, I was able to check the complete decklists of the two decks along with the set symbol and a scan of the new art cards. The Duel decks is set to be released this September 2nd. The decklists after the jump.
 

Ajani Decklist

Creatures (22)
1 Woolly Thoctar
1 Firemane Angel
1 Fleetfoot Panther
1 Loxodon Hierarch
1 Marisi’s Twinclaws
1 Spitemare
1 Qasali Pride Mage
1 Kird Ape
1 Canyon Wildcat
2 Ajani’s Pride Mate
1 Loam Lion
1 Nacatl Hunt-Pride
1 Wild Nacatl
1 Jade Mage
1 Ageless Entity
2 Sylvan Ranger
1 Essence Warden
1 Pride of Lions
1 Briarhorn
1 Grazing Gladehart

Enchantment (5)
1 Searing Meditation
1 Ajani’s Mantra
2 Recumbent Bliss
1 Griffin Guide

Sorceries (2)
1 Titanic Ultimatum
1 Lead the Stampede

Instants (4)
1 Naya Charm
1 Lightning Helix
2 Sylvan Bounty

Planeswalkers (1)
1 Ajani Vengeant

Artifact (1)
1 Behemoth Sledge

Lands (25)
2 Evolving Wilds
1 Kazandu Refuge
1 Graypelt Refuge
2 Jungle Shrine
8 Forest
6 Plains
3 Mountain
1 Vitu-Ghazi
1 Sapseep Forest
 

Nicol Bolas Decklist

Creatures (16)
1 Fire-Fiend Ogre
1 Moroii
1 Jhessian Zombies
1 Dimir Cutpurse
1 Igneous Pounce
1 Blazing Specter
2 Hellfire Mongrel
1 Slavering Nulls
1 Ogre Savant
1 Nightscape Familiar
1 Shriekmaw
1 Morgue Toad
1 Steamcore Weird
1 Brackwater Elemental
1 Surveilling Sprite

Enchantment (1)
1 Elder Mastery

Sorceries (6)
1 Rise
1 Pain
1 Cruel Ultimatum
1 Slave of Bolas
1 Profane Command
1 Deep Analysis

Instant (7)
1 Spite
1 Recoil
1 Countersquall
1 Grixis Charm
1 Undermine
1 Agonizing Demise
1 Vapor Snag

Planeswalker (1)
1 Nicol Bolas, Planeswalker

Artifacts (3)
1 Icy Manipulator
2 Obelisk of Grixis

Lands (26)
9 Swamp
5 Mountain
7 Island
2 Terramorphic Expanse
2 Crumb Ling Necropolis
1 Rupture Spire
 
The Duel Decks’ set symbol:

Here’s a camera shot of the new art cards, including the foil Ajani and Nicol Bolas.

Source can be found here.