The supply provider for the Zerg, the Overlord is also very useful now as a supporting unit because it can create patches of temporary Creep for the Zerg to walk on, or do other cunning things such as enabling Nydus Worms to invade an enemy base. It can transport units through an upgrade, as before, but to receive detection, it must be upgraded to an Overseer (for a meager fee). Keeping a proper mass of Overlords is key to building a large and effective Zerg army, they provide 8 supply each.
