The Reaver was once a robotic civilian transport, but when conflicts between the Protoss tribes escalated, they were weaponized by the Protoss and used as siege engines. Their microfactories can fabricate Scarab seeker bombs, which can blow away enemy units and buildings alike.
Using the Reaver: Reavers are very powerful in attacking, at the cost movement speed, rate of fire and armor strength. When deploying Reavers, make sure they are protected by Zealots/Dark Templar and Dragoons, and ALWAYS have them moved by Shuttles. If you use them right, they can level a heavily fortified enemy base in minutes.
Fighting the Reaver: Reavers are strong, and their bombs can take out a whole group of ground troops, while causing heavy damage to survivors. Attack in swarms to overwhelm them. Better yet, if there are few Dragoons or if you have enough air units, attack from the air.
Unit Class: Protoss Robot, Siege Engine.
Weapon: Scarab Bombs. High Damage. Low rate of fire. Manufactured by unit. Splash Damage.
Produced By: Protoss Robotics Facility(requires Robotics Support Bay).
'Strong Against:' Small Infantry groups(particularly Terran or Zerg), Buildings.
Weak Against: Large Infantry Groups, Mechs/Heavy Units, Aircraft.
Ground Armor: Increases armor strength of Protoss Ground Units. Researched at Forge.
Plasma Shields: Increases the strength of Protoss Plasma Shields. Researched at Forge.
Scarab Damage: Exactly what it says on the tin. Researched at Robotics Support Bay.
Scarab Capacity: Doubles the amount of Scarabs the Reaver can carry. Researched at Robotics Support Bay.