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|Unit||Number Hallucinated per Cast||Combined Hitpoints of All Hallucinations Per Cast|
Hallucination is a spell cast by the Sentry and it can be used both offensively and defensively. The spell creates one or more hallucinations of a Protoss unit (Carrier, Mothership, Observer, Dark Templar and Sentry excluded), that appear as an ordinary unit to the opponent. Hallucinated units deal no damage, have no active abilities, take double the damage their counterpart would take for all attacks, and do not have any health armor or shield armor.
Detectors (and scans) can expose hallucinated units, making them appear the same fluorescent blue color they appear to the casting player. If exposed by detection, hallucinated units will have a lower AI attack priority only getting attacked once all real units are dead. Neither EMP nor Fungal Growth will reveal the hallucinations, however.
Hallucination is not a commonly used spell in competitive play, as the Sentry's Guardian Shield and Force Field are considered more viable spells. It does however have four main uses in competitive play:
- Hallucinations (particularly of the swift, airborne Phoenix) may be used as a fast and convenient non-detector scout behind enemy lines. Especially in cases when the player opens with a build that does not provide a fast way to scout (specifically a Robotics Facility or a Stargate) like the 4 Warpgate Rush or a fast expansion, Hallucinated Phoenixes can be a very cheap and efficient way to get vital scouting information.
- Hallucinated units can be used to soak up damage on the front lines of a players army. A hallucinated Immortal does possess the Hardened Shield ability. However, due to the nature of hallucinations taking twice the damage, this results in 20 shield damage.
- A properly chosen Hallucination can make an enemy expect one tech line while the Protoss player chooses an entirely different one.
Hallucinations can also be used to encourage opponents to make poor tactical decisions in battle, such as flank and target a hallucinated Colossus with Zerglings or use an EMP on fake High Templar. However, this relies on the lack of detectors in the immediate vicinity of the hallucination.
- A hallucinated Colossus or any hallucinated flying unit can be used to achieve high ground vision. This is most commonly used to enable Stalkers to blink up to higher ground, or to enable warp-ins on high ground with the Pylon on the low ground.
 Vs. Protoss
Because Protoss forces do not have as much anti-air, especially when they do not detect it, a Hallucination that can convince the opponent to expect air will result in a great deal of wasted resources and tech on Photon Cannons and other anti-air. This forced tech switch gives the caster army a significant advantage as they may move in with a ground force that can easily overcome a handful of Cannons and enemy forces.
 Vs. Terran
Against a Terran opponent, it is possible to convince the enemy that the Protoss player is going for an air based build such as a Void Ray build with a few Hallucinations, resulting in the Terran player wasting some resources on Missile Turrets and anti-air while the Protoss marches in with a ground army. Hallucinated High Templars might potentially draw away an EMP from your real army. Typically though the Terran opponent has sufficient detection for such a plan to not work as efficiently as possible, and a Sentry is better off using its energy for Guardian Shields or Force Fields.
Hallucinated Zealots are also useful versus Terran going Mech. In a big engagement they can draw the first Siege Tank volley away from the actual units as well as possibly causing friendly fire to the Terran army. Hallucinated Immortals can also act as meat shields in PvT due to the fact that the can soak up a good amount of damage.
Hallucinated Phoenix can be used to drain energy from Terran Raven's Point Defense Drone ability.
Hallucinated units are sensed in the fog of war by Sensor Towers.
 Vs. Zerg
Because the Colossus is such a dangerous unit against a swarm of Zerg forces, Hallucination may convince the Zerg player that a Colossus tech is coming, while an unexpected High Templar or air-based force is in fact coming. The same could be done by forcing the Zerg to expect air forces, and then approaching with an entirely ground-based tech.
 In Combination with Other Abilities
- Point Defense Drones will activate on projectiles from hallucinated units.
- Hallucinated Colossi don't break Force Fields but walk through them instead.
- No hallucinated units can be picked up by a Warp Prism (or any other transport unit for that matter).