How many games have you played against the Swarm and gg'ed, because you were just overrun by Zerg masses?
How can you turn the odds against him?
What are the main problems against any Zerg player?
-Scouting problems (and therefore not knowing what the Zerg is up to)
-Dangerous Drops
-Simple masses of Units
-Lack of Detectors (Observers dying to Scourge and therefore giving no more detection against lurkers)
-Ultralisks
-Being contained
And that's about it. So how adressing these problems altogether?
Zerg's units have to be in masses to be effective. How fast do single Zerglings die? Do you fear 6 Mutalisks if you have 2 Cannons?
And that's where the Protoss advantages kick in. Once Zerg Units are grouped, they become vulnerable. Just use your weapons of massdestruction. PSI-Storm (but also Reavers) wait for a concentrated attack and then 4 well placed PSI-Storms cripple any attack early-mid game.Late Game? Just build more high Templars and storm even more.
Basically there are 2 phases for this to work.
Phase 1: Making the Zerg Units stack
*) In your own Base against a frontal attack: the best is to defend at a choke. If possible, narrow it with big buildings
like WarpGates.Place Photoncannons behind. Make the entrance narrow, so that the Zerg Units have to concentrate more. Leave little space inside your base to manouver for the Zerg.
*) When you're out on the battlefield, try using big fat troops, that can stand much damage. These are Archons, but also Zealots can stand much damage (because they are small and therefore get less damage from Hydralisks while doing full damage).Therefore forcing the Zerg to bring along a big army to beat that Archon-Zealot Army. The same concept works lategame with carriers.If you choose to use them, the Zergplayer will have to counter with mass hydralisks (if he goes for Terrors, there is a modification, i'll explain later)
Side note to Zerg armies flanking you: this isn't the problem, as long as the fat Archons gather groups of Zerglings around them, that can easily be PSI-Stormed. And Hydralisks are always quite easy to storm.
Phase 2: Mass Destroyers
Vs Zerglings either PSI-Storm or Reavers are good. Vs Hydralisks PSI-Storm is defenitely better.Thenn, you should have any kind of army (even small) to kill of the rest. Like I said just before, use Archons-Zealots.On open field, you can use Shuttle to transport your Reavers and/or high Templars.
Conclusion: So when fighting any Zerg Player, you'll need to be able to face large armies of Units. Because the Zerg's Minerals alwasy go to either Zerglings or Hydralisks or both, these 2 are the units that can be massed (this is less true for gas-expensive units). So dealing with them is a priority. And both phases are very important. If you don't make the Zerg unit's stack, he will attack at many different spots, and therefore your Mass Destroyers won't be effective. If you don't use mass destroyers, he will win any fight, because of superior numbers.
So this adresses the Problem of Zerg Mass Units.
If the Zerg decides to attack your bases instead of your army (happens quite often), directly or dropping, you should be able to hold off those attacks without your army. When you get a massive attack, this will be perhaps impossible, but the attack should cost the Zerg so much, that it will cripple him severly. If you want to do that, you have got to have a good amount of photon cannons and quite a bunch of high Templars. If you've got 6-8 Cannons +4-5 high Templars defending a base, it will cost the Zerg Player very much, if he decides to attack such a base. And what you defenitely should do is counterattack. Send just the necessary amount of units to finish off the rest of the attack (maybe a few archons and some zealots) while you should attack with your main force. If the Zerg has wasted his units on that attack, your Archon-Zealot Army will rape at least a base of him, while hopefully with the initial cannons and storms, backed up by a few units, you can hold his attack.
Lack of detection, lack of scouts, dangerous drops.
These are 3 other problems and maybe 3 reasons you want to build Corsairs. Air superiority is quite important for you.
Corsairs in adequate groups (8+) adress any Scourge and Mutalisks. Therefore giving Obeservers a longer lifespan. And also Corsairs are Scouts themselves. If you see it coming, they can effectively intercept any drop.
But these are not the only reasons why Corsairs are that important. They can engage Overlords quite well, and therefore turn the game around, leaving the Zerg without detection. Sometimes this gives an opportunity to use dark Templars very effectively. (Anyone remember Nal-Ra countering Mondragon on Blizzard WWI?)
Or late game, if you got the money to go for disruptor net, this will give you an additional bonus against a Zerg ground
army, by cutting their power into small bits.
Being contained and lurker.
If the Zerg uses just Zerglins, Hydras to contain you, feel free (if you have the units) to engage him as it would be on any open ground: Archon-Zealots backed by PSi-Storm and/or Reavers.If the Zerg players decides to attack your base, your detetors are photoncannons, and lurkers aren't that effective against cannons. Because then again they would have to attack in numbers, therfore rendering themselves vulnerable to PSI-Storm. If you want to break the containment, there will be 2 possibilites.If the Lurkers are few (<4), then just kill them directly with Archons and Zealots. Maybe soften them up with a PSI-Storm. But as soon as Lurkers become deadly to Zealots (this is when there are many lurkers), you can use PSI-Storm at will. Got an observer Killing PRoblem? Research either speed or sight range upgrade for observers.(if you don't have corsairs). If you have Corsairs, adress the problem itself by protecting Obervers against scourge.
Breaking out gets so quite easy. First have adequate detection.And then break out. If there are many Zerg Units, PSI-Storm, otherwise you should win any direct battle.
Ultralisks
They are about the same as Archons.They can take quite some hits, but so they do much less damage than Zerglings. So you
still take care of Zerglings as before. And once all his supporting army is dead (Zerglins and Hydralisks), you can quite easily overcome those fat beasts.
Dark Swarm
Just makes your ranged units unable to deal any damage. But as your main damage is dealt by PSI-Storm, Reavers, this shouln'd be a real issue.Also note that both, Zealots and Archons work under Dark Swarm.
Last but not least: Dark Archons.
They are quite expensive (if you already have all the above units). But once you can get them, it's nearly GG. Feedback any Queens (if some are used) and defilers. Maelstorm any bunch of Ultralisks or Air Units. And why not mindcontrol Queens, defilers, ultralisks, lurker??? But I would say that maelstorm (in combination with PSI-Storm) can be quite a game-winner.
Some last thoughts
Dragoons: I thinks a few can be ok. But why would you want them? The Gas is better used in templars.Because you will build them to attack lurkers, and here PSI-Storm is better. After a Lurker has been stormed once, it is good to have some Goons, to kill it, but for that purpose alone, you should not get too many. Their Gas should go as said in h.Temps or corsairs, their Minerals in zealots, Cannons or Corsairs. Maybe a reaver.
Dark Templar: they are good when used as surprise, when you got aircontrol with Corsairs.
How getting to all that? This is maybe the most difficult part.And i think there are many answers. From opening with a FE, to harressing with a 2Gate proxy-build, there are many possibilities. But as an easy rule, you should get a good economy running and perhaps start with getting a combination of 1-2 Corsairs and high Templar (which can be morphed into an Archon, if you suspect an Mutalisk attack).And if needed add Corsairs, otherwise go out, with that army when you are sure that you can keep your expansions (like I said before with PSI-Storm and Cannons). When being contained, try to do something useful: expand with a Shuttle (perhaps an Island, perhaps an unscouted base). Once the Cannons are up, and a few Templars are there, it will be pretty ugly for the Zerg to get it back. Or while being contained, make some high Templar drops do PSI-Storm his drones. Zerg players don't really appreciate that.
Ok. As anything, this isn't perfect and so I would really like to hear comments on it. If you have something constructive to say, well everybody would love to hear it. But if it is just flame, then you are just letting everyone loose his time.
BlackDevil
Edit:
As I see quite some sceptical minds here, maybe instead of pointing out that this post is not perfect,which helps nobody (anyhow, who can pretend to be perfect at Starcraft?), what about putting in some ideas of yours, like what you would do differently in certain situations, what units you will handle in a different way, and how?
Like that this thread is a starting point for a good discussion which will be useful for everyone.