StarCraft: Brood War/Protoss Mission 8: Countdown

Walkthrough
In this stage, you need to defend the temple at the middle of the map near the end of the game after two VIPs reach the temple. What you really need is a big bunch of armies surrounding the temple to make sure no one can reach it. To get those armies, you need to do the following step by step. Zerg is cheap and strong, especially for the Hydralisk, and it is a great advantage that it can attack ground and air units with average damage. Zerg Nydus Canals are a good transfer for reinforcement units.

Photon cannons are your best bet, supplemented later on by Corsairs and Scouts for the occasional Guardian attack.
 * Tighten up your base defense.

The most important part of this stage is to capture a drone and build up a Zerg force in either expanding base and defend the temple at the end of the game. Take over the red color Zerg base as soon as possible after you stabilize your base defense. Using mind control, capture a drone and make a base with it. Upgrade Hydralisk's stats, speed and range, to max.
 * Capture a drone.

On the east side of the map there are natural extension sites for you to gather the money you need for the defense of the temple.
 * Capture the only natural extension.

Make a lot of drones to gather the extra resources and build a lot of Spore Colonies and Sunken Colonies.
 * Build two hatcheries beside the temple.

Spawn Hydralisks with all your resources and fill in the blank in the middle of the map. If you have extra resources, buy some Carriers and park them on the temple. Anything that comes near the temple will turn into ashes.
 * Fill up the space around the temple.

Depending on how confident you are feeling, it IS possible to completely eliminate the Zerg from the map, but it won't be easy and it will take almost all of the available resources on the map. However, it will be worth it to basically win the level once your special units reach the temple.
 * Alternate advanced strategy

Build 3-4 Gateways, and mass Dragoons. Build 1 Starport to build some Corsairs for base defense against Guardians. Build at least 2 Rob. Facilities for Shuttles. Don't bother with Scouts/Carriers, as scourges and hydras will eat them alive.

You should be able to do some serious damage with 2 teams of dragoons. The teams will die often, which is why this strategy can be expensive, but it is effective and cheap to replace (compared to most Protoss units). Make sure to bring at least 1 Observer, since Lurkers will rack up damage fast. You will also want to bring some Corsairs to Disruption Web the Spore Colonies that completely surround the brown and orange Zerg bases, otherwise you will lose Shuttles during your attacks.

This is a tricky strategy to pull off, as it requires good resource management and good unit control (Knowing when to focus attack, and how to get as many of your bulky Dragoons firing as possible) but for those looking for a challenge, or just a more straightforward approach to the mission, this is it.

Alternate Strategy
If you aren't comfortable with the Zerg units or don't want to manage another tech tree, then a simple all-Protoss strategy is to ring the temple with Photon Cannons. Lots and lots of Photon Cannons. They're very cost-effective at 150 minerals and 0 gas. However, guardians can destroy them from outside their range, so keep a team of scouts ready to pound any that appear. Whichever strategy you choose, resources are plentiful at the temple, so spend freely on your defenses.