So, for a total of six mana, you can make Zack a respectable 4/6 with the Buster Sword equipped
I did say that I dislike Cabal Coffers and similar Mono Black Control lands in this deck, but lands that 1) enter untapped and 2) tap for B are always worth considering: Shizo, Death's Storehouse and Takenuma, Abandoned Mire are top on the list, but for colorless lands I think Nykthos, Shrine to Nyx can probably start ramping by turn 4 and Phyrexian Tower is worth testing too
The ultimate is no joke either, you do have to deal with Wrenn and Six else you are just going to eat endless Lightning Bolts from the bin and die to it
Every top leader has an ability you want to use every turn
Prominent from the dawn of MTG, dragons have had a whole MTG set dedicated to them in Dragons of Tarkir, and even gave rise to the popular Commander format, otherwise known as EDH or Elder Dragon Highlander