Remember the Warhound unit from the beta of Heart of the Swarm? Originally planned as a replacement for the Thor, the Warhound was removed because they became a very strong focus of the competitive scene and were simply too powerful.
Well, today they're back! Except, not as a buildable unit from the Factory. Nope, Blizzard has turned each and every race's workers into the Warhound. Everything except their skin and animations remain the same. They harvest minerals by punching them, which is pretty much the best thing ever. HuskyStarcraft has uploaded a video of the "new" workers in action, so check it out!