The first ability gives a creature +1/+0, trample, and haste for the turn, letting you swing right in with a creature you just played
The black in its color identity has kept it from playing a role in dedicated defender decks (which are generally Bant) up to now, but with Tarkir Dragonstorm, a new color combination has opened up the archetype to several new cards
Each Play Booster contains 14 Magic: The Gathering cards and 1 Token/Ad card, Helper card, or Art card
You can also blink this with things like Ephimerate, and it gets even more out of hand
Designing this set was very fun and exciting for those of us working on it
Spectral Sailor, Rattlechains, Shacklegeist, Supreme Phantom, and Lofty Denial provide a strong core no matter the particular flavor of Spirits you choose to build into