The vanguard are piloted by Tal'darim warriors that fell in battle. Disgraced in defeat, they are placed in a vanguard for one more chance to make up for their failure. They revel in causing as much destruction as they can before dying in service to their highlord.
The vanguard's normal attack is significantly different from the immortal and the Nerazimannihilator. The vanguard's scatter cannons deal damage in several attacks, allowing them to do significantly higher damage than the other immortal variants, but causing them to be more heavily penalized by armor. The vanguard also deals splash damage in a small radius around their primary target. This makes them very powerful against large numbers of armored enemy units, and can gives them the highest damage potential of the three immortal variants. However, they fire significantly slower than the immortal and annihilator, making them very vulnerable when facing superior numbers in staggered waves and/or unarmored/light enemies. Their attack also has a travel time, so it can partially miss fast enemies such as zerglings or charging zealots. Spreading out vanguards allows them to best utilize their show rate-of-fire shots on incoming waves of enemies.