A single Summer Mystery Box can be purchased from the store for 25 Farm Cash. There's currently no time limit on it (even though it does clearly say it's part of the Summer theme), so you might have a bit of time to save up those Farm Cash if you don't have them on hand currently. Either way, each box comes with one of six animals, but there's no way to tell whether you'll get a Ram or Boar (which would matter, of course, if you don't actively breed both). Here's what's available:
Purple Stars Ram
Leopard Brown Boar
Yellow Spots Boar
Yes, you're reading that correctly, this box contains a Candycane Boar, which can currently be purchased for 5 Farm Cash less in the game's store. However, since there have been two versions of this animal released - one in color-changing red and white [pictured] and another in blue and green - it's possible that you may have a chance at either. We're looking to confirm that. Still, even if you choose to negate that animal from the wanted possibilities here, there are still some fun patterns to be had, the stars and leopard prints being my two personal favorites.