Corsair/Dark Templar (vs. Zerg)
The term "Corsair / Dark Templar" refers to a unit combination. Depending on the underlying goal, it can be used as opening off one base, as reactionary mid-game transition after a Fast Expansion or as late game strategy. Both units support each other: the Corsair snipes Overlords and thus allows Dark Templar to attack expansions or units undetected.
- To read more on the mid-game transition, see also: Bisu Build
One Base Play
One Base openings using a Corsair / Dark Templar unit mix were popular in the earlier days of competitive Brood War. However, most Zerg players learned to adopt over time, rendering the strategy highly risky. In modern Protoss vs. Zerg this strategy is rarely used, but might be an option in a longer best of series.
There is no fixed Build Order for a one base opening, as the sequence of the building strongly depends on the reactions of Zerg. However, a general pattern can be listed.
The execution of a one base Corsair / Dark Templar opening varies a lot. Protoss needs at least two Zealots to be safe against Zergling attacks in the early stages, if he can defend on his ramp. Additional minerals can then be spent on a second Gateway faster, or for a Forge, which will be eventually needed to fortify a Natural Expansion.
The first Corsair should immediately be sent to kill Overlords. Which Overlord he targets depends on the Zerg reaction. If Zerg plays passively, the Corsair can target Overlords in the near of the Zerg base. If Zerg prepares a Hydralisk attack, the Overlord scouting the Protoss base should be targeted. If Zerg tries to transition to Mutalisks, the Corsair should be used with greater care.
Regardless of the Zerg reaction, the first Dark Templar is used to pressure Zerg. In case of a Hydralisk attack, he is used to chase away the threat in front of the Protoss base. In most scenarios Protoss will take his Natural Expansion and transition into an ordinary unit mix consisting of speed Zealots and High Templars.
If Zerg plays passively, a small attack with Zealots and the Dark Templar can be attempted. In an ideal scenario, Zerg will lose his Overlord, enabling the Dark Templar to attack the Natural Expansion. In other scenarios Protoss can try to sacrifice the Zealots and runby the Zerg's natural expansion with his Dark Templar, to go after the drones in the main base.
Regardless of the outcome, it's highly unlikely to kill a Zerg with a Corsair / Dark Templar opening in modern Protoss vs. Zerg. In most scenarios, Protoss will use the Dark Templar to maintain map control and only use it as harassing unit in optional cases.
Late Game Strategy
Regardless of the opening, Protoss can use a Corsair / Dark Templar mix in the ultimate late game, to counter a unit mix of Ultralisks and Zerglings.
As this strategy only describes an option in the late game, there is no more fixed Build Order possible. Instead, a list of requirements can be given.
The execution of a late game Corsair / Dark Templar mix is relatively easy. Usually, Zerg will try to challenge Protoss' map control by building up a massive army of Defilers, Zerglings and Ultralisks. None of these units can protect Overlords, which are now vulnerable to a larger group of Corsairs. Furthermore, without Overlords, the ground army can not fight Dark Templars and only few bases will be guarded by Spore Colonies. The only remaining option to detect Dark Templars for Zerg is to cast the spell Plague on the invisible units.
Usually Protoss will add a second and even third Stargate in a stalemate situation in the late game. Adding two more buildings is relatively cheap. He'll slowly train Corsairs whenever he uses units, or will sacrifice a low number of Zealots, while hiding the Corsairs for as long as possible. While Protoss prepares the switch, he will have less units on the battle field, which requires him to stay passive until the Corsairs are ready. Once a decent amount of Corsairs are ready, Protoss might attempt a small scaled attack with the old ground army against a less fortified Zerg expansion to free up his supply. Damage inflicted to Zerg by this attack is an optional bonus. However, a few units should be kept back to defend against direct counters. While the units die and the supply frees up, Dark Templars will be built.
This switch might be enough to kill the Zerg, but in most scenarios this is only a temporary fix, as Zerg can quickly add Hydralisks. The more the switch comes as surprise, the better it will work.
A Corsair / Dark Templar opening works on any map. In modern Protoss vs. Zerg, a one base strategy works best on maps enabling the Protoss to take a Fast Expansion in the back of his main base.