Hallucination

Hallucinate

A fun spell that sentries can cast, but it has to be researched from a cybernetics core for 100/100 first.

Hallucinate allows you to spawn hallucinated units that cannot attack and take double damage. Your opponent cannot visually tell the difference between real and hallucinated units without detection (though the fact that they aren't attacking will make it obvious real fast usually).

Above are the units that you can create with hallucinate. However, they spawn in differing amounts. Lower tech units spawn in more numbers. For a full list, check out this link.

Some uses of hallucinate:

1. Scouting. Spawn some hallucinations and send them off to scout for free. Some players will even research hallucinate quickly (from the cybernetics core) so they can spawn a phoenix ASAP and take a look at their opponent. Phoenixes also can give you high ground vision, which is useful for not just shooting upwards but allow safe blinking with stalkers.
2. Soak up damage.
3. Scare the enemy. Spawning several void rays and floating them near his base will scare the crap out of him. Mixing hallucinations in with real void rays will really scare him. This can be used to force him to build units/structures he doesn't want to or to call off an attack he'd otherwise have won.
4. Block movement. Just make some hallucinations and run them to a ramp or chokepoint to clog up the enemy. Even if they know they're fake, they'll need to shoot through them before they can proceed.
5. Crush force fields. WTF?

Yep. Colossi are massive units, and massive units crush force fields. Hallucinated ones do as well, apparently.