There are 16 Duels in the Single Player core campaign and you must win the first duel to unlock the next one and so on. Playing on Mage (Easy) difficulty definately speeds up the pace as opposed to playing on Planeswalker (Hard) difficulty.
You will get a first taste of Tezzeret's Blue-Black deck in Battle 14. I used the default Green "Teeth of the Predator" deck, took out all unneeded cards that I unlocked previously like Masimo, Wurm's Tooth to keep my deck card count low and didn't have any problems facing him. He plays alot of artifacts and creatures that compliment them and if he gets 3 of the 2/1 creatures out it'll be a race to see who can whittle down the opponent's life first.