Jay28It could be any Booster Box, as this is a grab bag product nothing is guaranteed other than the $150 getting a booster box from any set. The example said it MIGHT be a box of Shadows, but this is not definite. For all we know it could be Dragons Maze, or Origins, or Fate Reforged, or M13.
CylvreThe $50 and $100 drop levels state that there will only be standard legal booster packs in those. Makes me think that the $150 will only have a box of a standard legal set as well (unless you win one of the door prizes). Someone from Massdrop will have to confirm that though.