The official Starcraft 2 site has updated details of the Protoss Observer.
These small drones are employed to survey vast wasteland areas or observe and record battles for study within the protoss archives. Their complex sensor array leaves little energy for defenses, but they can detect cloaked or concealed enemies with ease. This ability makes observers invaluable auxiliary units on the battlefield.
Observers that are used for deep-space exploration are often deployed without any defensive systems. However, those destined for use in a combat zone are equipped with a micro-cloaking field to hide them from the enemy. The small sensor signature of an observer means that the drone does not have to drain its energy in order to maintain the field over long periods.
Artwork images show what looks like a Xel’Naga robotic unit, or defensive building. It is not quiet explained what it is, but surely doesn’t look Protoss. The unit remains underground. Legs extend outwards and walks like a dragoon. The strange part is that the robotic unit or building detaches its upper body and spins into the air going airborne.
Fans suggest this could be a protoss mine. What protoss unit will deploy mines is yet unknown.
It could also be a Xel’Naga unit.