The reaver has an extremely powerful attack, suited for destroying clusters of units with less than 100 hit points, such as hydralisks. It is an extremely important unit to the protoss army because the scarab has enough range to strike photon cannons, bunkers and sunken colonies without exposing the reaver to danger. Only tanks and air units out range it. The reaver only slightly outranges defensive structures, so they should be carefully watched lest the reaver over-approach.
Scarabs have a unique attack in StarCraft. Scarabs are built from the reaver itself, for a cost of fifteen minerals each. The reaver can store up to five (ten when upgraded) at one time. Often players will queue up all five as soon as the reaver is produced. The time to create a scarab is longer than a reaver's firing cooldown, so it is important to create new scarabs as soon as the reaver is no longer full. While they do radial splash damage, they do not harm your units the same way tanks do. Scarabs are the only attack that paths around the map and can get stuck on untargeted units or buildings. If the scarabs travel far enough, about a screen's width, they will explode and do no damage. Scarabs do not travel all that quickly, either. Workers can escape a reaver drop by moving away before the scarab is launched, ideally using worker harvest collision to a second base.
While the reaver is extremely powerful, it is also the slowest ground unit, has a long cooldown, and is quite costly. Shuttles are frequently used to move reavers to the front lines and to protect them from ground fire (see Strategies). Remember that a fully-loaded reaver costs seventy-five minerals above and beyond its base cost. Losing the shuttle as well is equivalent to losing almost three zealots and two dragoons. Reavers are also fairly easily to damage severely, given that they have 0 armor unlike most armored units and at 80 shields and 100 hitpoints, this is not defensively impressive for a protoss unit as zealots and dragoons have almost the same amount of shields and hitpoints.
One of the most popular mid-game protoss strategies is to use shuttles to drop reavers near enemy worker lines, where a single scarab can take out ten or more workers at a time. Protoss players will frequently plan this from the beginning of the game, particularly against terrans, building their robotics facility, a shuttle and a robotics support bay, and then a reaver as soon as the robotics support bay is finished. For serious harassment, shuttle speed is fantastic. However, the reaver/shuttle is a very big investment, so the harassment is a huge risk - losing them cedes a big advantage to the enemy. When using this strategy, it should be noted that unlike other units reavers do not immediately attack when exiting a shuttle or other transport, and will wait a moment before launching a scarab.
During the reaver's long cooldown it can then be picked up and hidden inside the shuttle. This effectively nearly doubles the reaver's durability, splitting attacks between the reaver and the shuttle, forcing the defender to bring air defense, and gives you time to reposition the reaver. You can also easily flee, leaving the defender to worry where you'll show up next. Expert players will use the reaver's attack to draw forces, and then use the shuttle flee to another worker line where they can continue the harassment.
Because a shuttle can hold for other slots of units, a zealot, dragoon, or a second reaver is frequently brought along as well. Against terrans, a zealot is dropped first to draw siege tank fire and any spider mines laid as a trap. A dragoon provides additional low risk harass, and is more flexible then a zealot. A second reaver provides the potential for significantly more damage, usually with the scarab damage upgrade, both to help take out buildings and to absorb more hits. If their attacks are timed properly, two reavers can keep up a continual barrage of scarabs, one firing while the other prepares its next shot. This both keeps the two covered from enemy counterattacks and helps prevent them from wasting scarabs attacking the same target.
Mass reavers are even more deadly. Reavers are deadly backing up zealots and goons. Shuttles can be used to keep reavers with the main army, and to get reavers in perfect flanking positions.
Mass reavers and shuttles (3+) are also commonly defended by mass corsairs (5+), particularly against zerg. This is one of the most mobile armies in the game; the corsairs protect the shuttles and use disruption webs to protect the reavers from ranged attacks, while the (6+) reavers can wreck a base in seconds, and then hop over to the next one. While a common strategy, particularly on large, macro-oriented maps, it's also one of the gutsiest strategies, and is very vulnerable to a surprise counterattack while traveling. Losing some or all of the force can also end the game in seconds.
Against reavers, spreading out one's own units to minimize the splash damage of Scarabs, and try and surround them from all sides. If they are escorted by a shuttle, preemptively getting air defense can frequently deter or eliminate a reaver drop before it happens. Reavers are very expensive, and if you can focus fire one, particularly with ranged units, it usually will swing the battle and give you an opportunity to counterattack.
Each scarab does 100 normal damage, upgradable to 125, plus splash damage. Scarabs will chase their target on the ground, self-destructing harmlessly after five seconds if it cannot make contact. Scarabs cannot ascend or descend from cliffs, but may use ramps. Scarabs may not be intercepted.