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 reavers and dragoons/hydralisks are necessary. The reavers can take out the base by themselves, while the dragoons and hydras are there to provide cover. Then, get a hatchery going. Here, you'll find a bountiful vespene geyser and plenty of minerals if you attack quickly enough. Wait for your resources to start coming in, and in the meantime, ensure that all your upgrades at the forge and cybernetics core are at least at level 2.

When you have sufficient resources, prepare your attack force. You'll need 24 carriers; that's right, 24 as well as some secondary units to provide cover against scourge. This will take up over 2/3s of your supply and use up almost all your resouces, so feel free to discard any excess you don't need and try conserving your money.

Once you have the said strike force, send your carriers down towards the Khalis. You will meet EXTREMELY heavy resistance in the form of dozens of scourge and plenty of hydralisks and mutalisks. However, once you break through to the Khalis, the brown zerg will not put up as much resistance as in the start. Wipe out all of brown's structures and then wreck the yellow zerg bases. Destroying all of the zerg on the map will take around 10 minutes and get ready to lose almost all your carriers, but if you're careful and patient, you will wipe the whole map clean. Then at this point, it is your choice to either send a probe to the Khalis or kill the overmind.

Alternate Strategy
If you don't want to take a huge risk with the above strategy, this one will suit you quite well. 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 than razing the whole map.