There are also two different layers of individual progression that can be unlocked via completing specific hero challenges. (digitalchumps.com)
For veteran players, the Training Arena will be open, allowing players to practice against specific heroes with specific movesets. (gamingtrend.com)
Alongside The Underhollow, Valve are also offering Cavern Crawl (a meta - game for unlocking new items by playing specific heroes in regular play) and Mutations. (pcgamesinsider.biz)