Overseers are genetically-altered overlords that have a mass of additional sockets filled with highly evolved optical receptors with hypersensitive retinas. Unlike most other zerg breeds but like overlords, overseers have the ability to act with appropriate judgment, but are severely limited in their mental flexibility.
Primal zerg packs have adapted overseers into their genome, but they are among the rarest breed of the primal zerg.
The zerg are obsessed with detecting subtler motions and more advanced camouflage techniques. The overseer's "eyes" have been through many iterations, each developmental cycle improving upon the preceding one’s optical evolution. That said, the first batch of overseers ended up crippled and blind when the arrays of microscopic filaments (relayers of sensory and spatial data) located on their vestigial legs gained sentience and became ravenous to the point of consuming the appendages that housed them. To correct this situation, the legs were excised and the filaments were transformed into long, fleshy tendrils grown from the overseer’s carapace. Now, when the overlord is subjected to the overseer strain mutation, its eyes melt into a luminescent substance that floats inside a semi-transparent skull. Sensory tentacles and twin photoreceptors, capable of sight in any environment, sprout from said substance, in between the openings of their thick, armored "faceplate". To further enhance the creature’s capabilities, the main body expands and grows six new hypersensitive optical receptors in strategic positions. This latest evolution allows the overseer to detect any hidden enemy units, including those that are burrowed underground or cloaked. The fins and tendrils of the Leviathan Brood overseers are bred to specialize in reconnaissance, allowing them to cut through both air and water with minimal effort.
By incorporating terran DNA into the overseer’s genetic makeup (particularly during its later stages of pupation), the creature displays a peculiar evolution pattern. Its creep glands expand and turn into stores of sentient, unfertilized bio-matter, and its organs no longer liquefy into creep, but instead a nourishing paste. At the overseer’s will, this paste bonds with the bio-matter in the sacs and quickly becomes an insidious infiltrator known as the changeling. Additionally, the bio-matter grows and solidifies at exponential rates when exposed to foreign atmospheres. The Swarm has capitalized on this trait, using its overseers to disable critical facilities in the midst of an invasion.
The overseer will gain the oversight ability in an upcoming patch, which roots it to the spot, but gives it 25% extra vision. This will ensure that overseers aren't unintentionally clumped with "F2" army commands.
Kill 5 Changelings in a single Unranked or Ranked game.
This achievement is a reference to Team Fortress 2's Meet the Spy video as an introduction to the class 'Spy', who could disguise as enemy players, but also instant kill via backstab and disable buildings (which aren't things the changeling is capable of).