2 new heroes; Slark the Murloc Nightcrawler and Kaldr the Ancient Apparition. From my thorough and extensive testing, I have no doubts Slark will get alot of play in weeks to come and by thorough and extensive testing, I mean 1 round of DotA.
Also…
IceFrog’s way of wishing all the players Merry Christmas I guess. 
Changelog and download link after the jump.