Diablo III's Reaper of Souls expansion is adding all kinds of new features and doodads, including a new Artisan. Blizzard recently detailed the new Mystic, named Myriam Jahzia, who will let you customize items with special enchantments and transmogrification.
In a lengthy blog post, Blizzard explains the two ways the Mystic can help you.
Enchanting lets you pay a material cost to alter stats, helping them keep pace with your current level. The Enchanting window will let you alter individual properties, and you can re-roll to impact the chosen properties as many times as you'd like. But, once you've enchanted a property, all the others are locked and only that one can be altered from then on. The enchanting is kept somewhat random too, so you'll be taking a gamble on your new item. If you want your prior item back, you can purchase it in a buyback menu.
Transmogrification, on the other hand, is all about style. It lets you pay some gold to change the appearance of any item, including Legendary and Set items, without changing their stats. You'll be able to unlock visual flourishes, and once unlocked you can access it across any characters. Common, Magic, and Rare items will unlock as the Mystic levels up, while Legendary and Set item appearances will have to be identified. Plus, Hardcore will get its own unique appearances to set you apart from the pack.
This is really more of a reintroduction, as the Mystic was originally in Diablo III but was later removed a few months before release. "We hope she'll be able to join your caravan in the future," the team said at the time, "but for now we're going to focus on the extensive customization options the game already offers." The future is now, people.