Treasure Chests in paper Magic

From November 26 through December 17, stores around the world will be able to host Standard Showdown tournaments on Saturdays with special promotional prize boosters earned through undefeated play. Apart from performance, Wizards suggested distributing them as prizes for new players.

Stores will receive 40 prize boosters (ten for each event). Additonally, stores can also get 44 Standard Showdown Boosters to use as buy-a-box promos over the holiday season. Each purchase of a Kaladesh Booster Box will get you two boosters and each booster contains three-cards:

• one premium Standard legal card, including Zendikar Expeditions and Kaladesh Inventions, not including double-faced cards.
• two Standard legal rares or mythics (Battle for Zendikar through Kaladesh, excluding Oath of the Gatewatch and double-faced cards).

Zendikar Expeditions and Kaladesh Inventions appear in roughly 1 in 33 boosters.