StarCraft: Brood War/Protoss Mission 6: Return to Char

Walkthrough
You start with two bases in this mission; a Protoss base and a Zerg base. They are very near each other, so it is easy to support each base when you need to. Once you start the game, you will notice that your Protoss base has many mineral fields, but does not have a geyser. Your Zerg base does have a geyser, but it only has a five-mineral field patch. You need miners from both bases to establish your economy.

Now take a look at your starting Observers; the one on the west side shows you two burrowed enemy Lurkers, and the one on the east side shows you a small mineral patch with a geyser. You have another Observer near your Forge. Lurkers are large-sized ground units evolved from Hydralisks, and they will attack you while burrowed. The Lurkers will probably make you jealous because you can't make them yourself... yet.

You should expand at your small base quickly for more gas. It is ideal to build a Zerg base there, since the area is both closer to your Zerg base and you can get Drones more quickly than Probes. You can support this base with Photon Cannons, but build them up the cliff.

Your next expansion should be to the west, where it is occupied by Orange Zerg. A group of Dark Templar and Hydralisks are necessary, and you need to keep bringing those waves since the enemy will support that base with more force. Now you are set for your resources.

Now that you have enough resources, start building your attack force. Support the last expansion you took. At this point, it is probably easier for you to Strike the Overmind than to go for the Khalis Crystal. That is because most of the land to the south (before you get to the Overmind) is empty, if you travel by air. However, travelling via the ground is much more difficult to do. Therefore, you should plan out an airdrop attack backed up by Scouts. A full group of Dark Templar and Hydralisks each, and a group of Scouts will do. Put all your ground attackers in Overlords; they are both cheaper and stronger than shuttles, and they will not eat up your supplies, but rather provide you with them. Let the Scouts take the lead, and have them take some damage while your Overlords drop your units. The Scouts should clean up the Guardians around you. After your units are dropped, just have them mass attack the Overmind.

Alternate Strategy
As above expand as fast as possible to the second geyser below the zerg base. But you can almost ignore the whole protoss base and everything west of it. Just put enough units/cannons on the west entrance to fight off the occasional few hydralisks coming that way.

Now build 3 hatcheries and keep producing hydralisks, don't forget to upgrade them. Two or three groups of hydralisks should be enough to push at the brown zerg player to the south. You should send all hydralisks produced in your base to support the attack. Then you should be able to clean the winding path to the Khalis crystal with ease. Then just send a drone there. This strategy is probably faster then going after the overmind.