The warhound is an anti-mechanical unit that was originally supposed to be available in skirmish games. It was expected to be a core unit in terran vs. protoss games due to the latter faction's reliance on mechanical units. It was of limited use against the zerg however due to their complete lack of mechanical units. It did not have an anti-air attack.
The Warhound remained as a campaign-only unit used by the Terran Dominion and is first encountered during Kerrigan's reclamation of Char. General Warfield used many of these to defend his headquarters on the planet. There were many on Korhal when Kerrigan attacked.
The warhound's unit portrait depicts a surly, military commander figure—akin to a toned down version of the battlecruiser's unit portrait. The warhound also has the ability to dance.
As of June, 2012, the development team was looking to find a way to make the warhound useful in terran vs. zerg matches. However as of September, 2012, the warhound has been completely removed from the game. The development team originally did not clearly state as to whether the warhound may or may not have returned later in the beta, but as of March, 2013, with the closing of the beta, it has been permanently removed from multiplayer but was eventually used in the campaign.
Heart of the Swarm beta files indicate that the warhound was once called the "titan mech." This mech had both a land and an air mode.