Zeratul is a commander for the Co-op Missions mode. He brings the power of xel'naga-enhanced protoss to bear against his enemies, and can utilize xel'naga relics to turn the tide in his favor.
Zeratul can deploy to the battlefield as a hero and can build advanced protoss forces augmented with xel'naga technology. Scattered through the map are a series of random artifact fragments Zeratul must collect. Using prophetic vision will give Zeratul a hint as to its location. Once it is found, it will give Zeratul new upgrades and top bar abilities.
Zeratul's top bar abilities are customizable, and each tier has options to select from. Zeratul can call down Legendary legions to help him in battle, which cannot be directly controlled but directed to locations. Zeratul can also utilize these customizable top bar to augment his army with passive abilities or new calldowns. Upon gaining all three artifact fragments, Zeratul can call down one of two xel'naga constructs, the Avatar of Form or the Avatar of Essence.
Zeratul acquires the following talents as he levels up.
Power of the Xel'Naga
Zeratul has a 100 starting supply and his units have increased life and damage. Buildings do not require pylon power and units cannot be warped directly onto the battlefield. Zeratul's ancient nexus can automatically construct ancient assimilators.
The Avatar of Form gains the ability to summon Charged Constructs that can individually cast miniature Psionic Storms. The Avatar of Essence gains the ability to transform all enemy units in a large area into a lower evolutionary form.
The designers of Co-op have stated that they always had been huge fans of Zeratul as a character in the StarCraft universe, and wanted to bring him into Co-op Missions.. However, there was already a “Dark Templar” commander in Vorazun, so care was taken to differentiate him.
The team wanted him both to be on the field as a hero and have a small elite fighting force, as he was most often featured in insurgent-style missions in the StarCraft II campaign, but to go beyond his singular identity as a dark templar. Throughout the campaign, Zeratul looked to the wisdom of the xel’naga for guidance, obsessed with finding their prophecies, and as such the idea to have him hunt xel'naga relics to aid him was made.
In addition, the team was committed to creating a commander that felt and played differently from his protoss brethren. To that end, Zeratul’s army was given xel'naga enhancements, with the intention of making him feel as much of a xel'naga commander as a protoss commander.
The Legendary Legion mechanic was inspired by Zeratul's propensity to have allies sacrifice themselves to aid him in the campaign.