The Overseer morphs from the Overlord and provides detective capabilities. It is faster and has more spells to choose from as well. Using the Changeling, you could scout an enemy base with impunity, providing your opponent does not notice it. It can also spread Creep enabling you to spawn Nydus Worms on Creep, an ability that enables surprise invasions or harassment. The Spore Cloud ability is used to block line of sight at a target area, again making the Overseer a must have unit for conducting ambuscades.
