Dragoons are seen only in StarCraft 1. They are ground based ranged units equipped with a phase disruptor. In StarCraft 2 the Dragoons get heavy shields that protect against heavy enemy fire, but are vunerable to weak enemy attacks. They also are equipped with 2 phase disruptors. These new improved Dragoons are called Immortals. They both are machines that house injured protoss veterans. After the loss of their hometown, Aiur, the shrines that made these Dragoon exoskeletons were overrun by the zerg (so if there is a StarCraft 3 [which I hope there is] that there probably won’t be any Dragoons or Immortals.) Also, there is also the new Stalker unit that can blink or teleport a short distance away form the original place. The Stalker unit is a ground-based unit that can attack both ground and air with its chronal web. Also, these Stalkers are also called “Dark Dragoons” and are the Dark Templar’s version of the Dragoon (see the templars.)
Above: They are Immortals. Below-Left:That is a dragoon.
Below-Right: That is a Stalker.
Above is the blink ability of the stalkers.