StarCraft/Protoss strategies

Hallucinating units
Hallucination (hotkey L) creates two duplicates of the target unit which do no damage.

Operational details & properties:
 * Hallucination works on both allied and enemy units; in either case, the hallucinations are marked as the caster's allies.
 * Hallucinations are instantly destroyed by any spell except Hallucination.
 * Some enemy spells, such as Ensnare, can vaporize multiple hallucinations in one cast.
 * Hallucinations lose HP/Shields twice as fast as normal units and have neither weaponry nor armor.
 * Hallucination forces an enemy to divert focused fire either upon fake units or spreading out the firepower.
 * Fresh duplicates can be created from other hallucinations.
 * Hallucinations do not produce anything and do not cast spells, which make hallucinated Reavers, Carriers, and spellcasters very poor and easily identifiable imitations.
 * New ones appear out of nowhere, and players may be able to keep track of them.

Hallucinations serve two purposes: To deceive enemy players and to deceive the AI:
 * Enemies may waste costly spells on Hallucinations.
 * Hallucinations appear to attack and thus attract enemy units.
 * Hallucinations also serve as decoys, drawing the enemy's attention either to a distant place on the map or forcing the enemy to make poor decisions.
 * The superior numbers that this skill may grant can intimidate an opponent.
 * Hallucinations also serve well as scouts and cannon fodder, in which case their effects may be doubled by separating the two dittoes.

Special hints:
 * Hallucinated Arbiters are particularly cost-effective if grouped with a real one.
 * Hallucinated Arbiters can be defeated with a well-placed Stasis Field.
 * Beware accidentally using this spell on an Interceptor instead of the Carrier.

Reaver dropping
This requires a substantial investment in tech, up to the Robotics Facility and Robotics Support Bay, which can't realistically be done without dividing one's focus on more standard base defense; but once prepared, if the enemy has not developed comprehensive defenses, can still wreak havoc, even with a small-scale expedition. At least one shuttle and typically one or two reavers are produced; as soon as the reavers are ready, scarab production is begun, the reavers are set on a control group and loaded into the shuttle(s). A safe route has preferably been scouted out, along which the shuttles are flown, away from the attention of any enemy forces, around to the back of an enemy base; the reavers are then dropped on the enemy base, typically beginning near the production pile, behind the minerals or even between the minerals and base, directly among the resource gatherers. Additional scarab production is begun as soon as the reavers are out. The reavers fire their scarabs at the resource gatherers, which are typically tightly congregated and particularly vulnerable to the scarabs' splash damage. A dramatic number of the resource gatherers can be wiped out in a surprisingly short time in this manner, crippling the enemy's economy. The inexperienced often have their defensive forces heavily concentrated in a forward position in anticipation of a land attack, although this becomes less typical as the game advances. The enemy then tries to summon the defending combat units back from the forward position to the production pile area. Even then, however, it is often surprisingly effective to load the reavers back onto their shuttles (giving the command to the reaver control group, rather than the shuttle, for a speedier upload), fly the shuttle to the opposite rear corner of the base, and unload them again; any ground units that have been gathered toward the reavers' original location have to traverse the typically very densely packed central base to approach the reavers again. Because of the reaver's significant investment, it is also often worthwhile to pack up the reavers and fly them off in retreat if they sustain significant damage, rather than let them fight to the death, then use them again a bit later when their shields have restored.

Reaver Drop
A reaver drop can be effectively defended against by providing defensive capabilities surrounding all sides of a base, and maintained in close proximity to the production pile itself, so an airborne attack force will not be clear of the defenses upon penetrating to the core of the base. Photon cannons or sunken colonies placed in immediate proximity to the mineral pile is often an effective defense.

A reaver drop can be paired with complementary units, at the expense of additional time and production prior to deploying the reaver drop expedition. Zealots, dragoons, and dark templars are all useful in helping defend the reaver while it provides the brunt of offense, particularly by keeping them close to the reavers.

Keeping the reavers well-positioned is also very important; they can be fairly idiotic if left to move around on their own; often it works well to keep them stopped in a particular spot and just let the scarabs fly.

An observer is often an indispensable companion for the reavers.

High templars can be very effective when dropped together with reavers, although this operation requires an intense level of rapid micromanagement. Corsairs are a favorite pairing with a reaverdrop; not only can they help keep the skies clear above the reavers, and defend the shuttles in flight, but their disruption webs and the reavers' scarabs are a perfect complement for a devastating attack. This is particularly true when facing siege tanks, one of the reaver's deadliest foes, but which suffers horribly under the influence of both a disruption web and an angry reaver.

The reaver drop was popularized in tournament games in 1998 by the player known on Battle.net as Zileas, then an underclassman at MIT, whose quickness with coordinating the reavers and shuttles were described as "like a shuttle that fires scarabs". This technique effectively prevented many ground-attack units from engaging the reaver, since it could drop, shoot and load back into the shuttle before they could counterattack. The developers of Starcraft, in a later patch, responded to this by introducing a short delay to prevent the reaver from opening fire as soon as it hit the ground.

Reaver Recall
A variant of the Reaver Drop is the Reaver Recall, in which an Arbiter's recall ability is used to immediately transport Reavers (and possibly other units) into the enemy's base much like Shuttles. This saves the trouble of building, loading, micromanaging, defending, and unloading Shuttles, but at the same time, drastically reduces the attacker's ability to retreat. This can be solved by using dual Arbiters. One Arbiter is used to recall Reavers to the enemy base and after they have unloaded their scarabs, an Arbiter back at the base is then used to safely recall this assault group back to the base. The Arbiter also provides cloaking to the Reavers. Of course, this strategy is both slow and expensive compared to the regular reaver drop. The best defense against this is to stop the Arbiter in the first place, but Zerg Lurkers with Overlords or Spore Colonies to detect the Reavers best exploit the tactic's poor withdrawal capability. Terran can accomplish something similar with Siege Tanks in siege mode and Missile Turrets or Science Vessels to provide detection.

The Reaver Recall is much less practical than the drop. After building a cybernetics core, the Executor has three choices- Templar, Air units, and Robotics. The drop requires one tree, while the recall needs all of them. (robotics for the reaver, air for the arbiter, and templar because it is required for the arbiter tribunal.