"Crown Crates are purchased through the Crown Store, and contain a randomized selection of useful consumables and collectibles that are valued more than the price of a single crate. In addition, they also offer a chance to obtain unique cosmetic items, pets, or mounts. Crown Crates include new and exclusive items, as well as some items you might have missed in previous limited time offers. Whenever you purchase a Crown Crate, you will always be awarded four items, with the chance to get a fifth item. In the event you receive a mount, pet, costume or personality that you already own from your Crown Crate, you'll be awarded a new resource - Crown Gems - in its place. You will also have the option to convert several items obtained from Crown Crates to Crown Gems any time you want. Items that can be manually converted include potions, poisons, riding lessons, experience scrolls, and other utility-type items. Any Crown Gems you earn can then be used to purchase the collectible items of your choosing from the current Crown Crate season."
These gambleboxes are going to run 400 crowns apiece (or four for 1500 or 15 for 5000), and this first season's major rewards are pretty sweet storm-themed mounts, auras, and emotes.