Tested on-cart and found Mat Block does protect against Boomburst. I consider this a good thing personally because not being able to defend against your own Boombursts with Protect or Substitute makes the move sound really unappealing to me. Unfortunately it's kinda predictable since both Mat Block and Boomburst have narrow distribution, so I don't see it going too far.
At the same time though, breaking the ears of two of the opponent's mons and one of yours is technically a win I guess.
At the same time though, breaking the ears of two of the opponent's mons and one of yours is technically a win I guess.