In the last game’s update one of the curious users have found some files associated with the Valve’s New Year event. Snow map textures, unique audio tracks and other stylistic elements labeled "Frostvirus" appeared on Monday. After this was announced a sale in a game store, where users can purchase unique Dota 2 hero items.
And tomorrow starts the "Greeviling" event, in which the main objective will be destroying the new forest creeps that stole various items from the shop. To take play and take part in the competition you need to buy dota 2 beta key or try to gain it in our January event.
More info you can learn from the trailer below, as well as on the official Dota 2 site.