The Mystic can enchant items, improving or modifying their stats in some unknown fashion. The Diablo 3 team hasn't given any specifics about what enchanting actually does, but they've said that players will probably want to enchant every item they can, so it's evidently a highly desirable bonus.
The first mention of "enchanting" came from the Caravan FAQ, released in August 2010 at the Gamescom expo. There was just a single line about the Mystic:
- The mystic creates scrolls, potions, magical weapons, spell runes, and charms, and can also enchant items.
A quote from an interview with indiablo.de at the same event confirms that the bonuses are not random:
- "There’s a fixed number of added bonuses. Enchants work like Gems. We wanted the enchant to do what it does each time, rather than force players to use the enchant over and over again (on the same item)."