1x factory sealed box of 24 Double Masters boosters including two non-foil borderless showcase box topper cards in each booster box.
Each booster contains 15 cards includingtwo raresandtwo foil cardsper pack! (And, yes, those foils can be up to two additional rares.)
From Wizards' website:
We've doubled everything aboutDouble Masters. Double the rare slots, double the box toppers, double the first-picks in Draft.
In addition to double the rares and foils in every pack, every box ofDouble Masterscomes with two (TWO!) non-foil showcase box toppers, which are pulled from a pool of 40 fan-favorite cards in beautiful full-art treatments.