We iterated a lot to get to the proper set size and the specifics of the draft format right, but Corey's going to cover some of that and a bunch more in his article, which covers the set design and play design processes in depth
The other thing about Spirits being a typal theme is that as more cards are printed that let you choose a creature type to get benefits, there will always be cards to pick up to improve your Spirit deck
Read the official preview from WotC and IGN.
Jund Turn 1: Play Blackcleave Cliffs, Inquisition seeing Thalia, Guardian of Thraben, Thalia's Lieutenant, Mantis Rider, Reflector Mage, Horizon Canopy
Its especially powerful against a player whos looking to play a small numbers of strong creatures as opposed to going wide
$450 Qty