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This level can be very challenging, so save early and often. When you first start BWZerg4, the map looks like it is long and thin. This impression is misleading. When you start exploring it you will realize that the map is actually the same distance as many other maps, but that the length from east to west is very long. At times it seems like it will not end. This feeling is reinforced by the way the map is jammed full of enemy units and structures.
If you have infested any Terran Command Centers in Zerg Mission 3, save the game as soon as you get into this level and hold onto this save data. If you select the level from the start screen, you will have the 10,000 minerals, but you will not have the Infested Command Centers.
Quickly, very quickly, evolve the Creep Colonies into Sunken Colonies, move the Overlords out to the perimeter of the base, evolve one of the Drones into an Extractor, set the other five Drones to gathering minerals, evolve one of the Hatcheries into a Lair, evolve all eggs into more Drones, set up a hotkey for each Hatchery, and set up a rally point for each Hatchery. The first event that will occur is that an enemy Ultralisk will attack as soon as it is discovered. One Ultralisk and the two Sunkens will probably be enough. There are three ways into the main base: north, west and southwest. Place a row of at least four Sunkens across the area west of the Star Wars-like toothy opening in the sand to shut off attacks from the north. Maintain a small force in front of these Sunkens, namely Hydralisks and Zerglings. Place more Sunkens near the ramp that is in the center or west, and place a few Spore Colonies here and there to be safe. But don't forget to keep building up your ground/air forces during this period.
One of the problems at the beginning of the game is the lack of gas that is accumulated. Although you start with 10,000 minerals, you are only given 500 gas. With all the building and upgrades, gas becomes critical. Make sure that there are enough Drones gathering gas. Queens will quickly become necessary for defense. Groups of Terran forces will attack, mostly with Marines, Medics and Firebats. At first the Tanks will not be able to get into siege mode. Being able to broodling Siege Tanks and/or Goliaths may quickly become necessary. Alternatively, large groups of Zerg will attack with as many as 6–7 Ultralisks (sometimes it seems like more). Being able to broodling Ultralisks will be even more important than against Siege Tanks. Zerglings just don't have the same effect they do against Ultralisks that they do against Tanks/Siege Tanks or Goliaths. One of the early attacks will be a force of 3–4 Guardians. A group of Hydralisks will be needed to destroy them.
The ideal way to win this level is with the Zerg rush. The way to effectively use the Zerg rush is to have the Hatcheries (or Lairs/Hives) hotkeyed. After building a sufficient force at the southwest entry area, begin moving them into the Terran/Zerg mixed base along the southern edge of the map just west of the main base. Never target buildings or units, unless there is only one unit that threatens you in particular. Move groups into an area, and let them decide what to attack. Using the hotkeys, change the rally point for three of the Hatcheries to be inside the area of conflict. Create mostly Zerglings and a few Hydralisks and Ultralisks (Zerglings are the easiest to make, considering you have many minerals but little gas). (Create forces with the fourth Hatchery, but have the rally point near the central access point to the west.) It is surprisingly easy to wipe out this southern base. If you are quick enough, there will be some minerals and gas left. Place your forces at the choke point in the west of this southern base just out of the range of the Siege Tanks that are defending a couple Factories and a Barracks. A force of Ultralisks and support forces may attempt to wipe out the force defending this area, so it is important to keep an eye on it. Scramble Queens to help in the defense, and build up the forces a little more.
Strategically place Overlords along the perimeter of your newly acquired area. You will need to know if a large force of Ultralisks or Siege Tanks or Battle Cruisers are about to attack. Scrambling Queens or Hydralisks (or even Scourges) quickly enough to limit the damage is vital. Send a group of Zerglings to the first baselet in the north and destroy the Missile Turrets and Bunkers and whatever forces are there. Usually the Bunkers are empty and there are no forces. There is a large mineral field and a gas vent here. Move the rally points of the Hatcheries (after the southern force is large enough) to the area in the center that will be able to defend the main base and the newly acquired land in the north from ground forces. Use the Zerg rush strategy to attack the units and structures in the center of the map. There are three more mineral fields and two more gas vents across the center of the map along the northern edge of the map and one very large mineral field just west of the new southern base.
Put off building a new Hatchery as long as possible, but don't wait beyond when minerals get to 1,000–2,000. If you can afford to build two new Hatcheries in the newly acquired areas at once, you will be well on your way to winning. There seems to be trigger points in both of the areas (north and south) that involve the building of Hatcheries. As soon as the Hatchery appears, attacks may come. Using the Zerg rush to wipe out the center of the map becomes a good way to defend all of your bases. If your forces can wipe out most of the center of the map and gain control of an important choke point that leads to the last Zerg and Terran bases, it will be difficult to lose this level. Build bases at each of the mineral fields along the north. The last base you should build is one from which you will gather minerals from the large mineral field west of the small southern base that you first took from the Terran/Zerg. Build it just north of the plateau that forms the northern boundary of the small southern base in order to avoid any trigger points.
Once you have control of the choke point that leads to the main Zerg and Terran bases, there may be attacks from Battle Cruisers and Wraiths. Be prepared with groups of Hydralisks and Spore Colonies (Wraith are very likely to use Cloak) that can defend the base being attacked. Scramble whatever else is handy in order to destroy the threat. Plaguing the attacking force is always a good idea. You will need to make a decision. Keep building Zerglings with Hydralisks/Ultralisks as support, or just build Hydralisks. A group of upgraded Hydralisks can destroy any air unit and can do a lot of damage on the ground. Their one weakness is against groups of Siege Tanks. A group of Queens and Guardians should take care of them. Queens will also be necessary during the attack on the Zerg base, since there are several Ultralisks that are kept back for defense. You will definitely need to attack from the air on the Zerg base, considering the base primarily consits of anti-ground defenses. A large portion of their base is composed of Ultralisks, Lurkers, Guardians and Sunken Colonies, so you will need many Guardians and a few Mutalisks to handle this base.
Move Guardians and some Mutalisks along the northern edge of the map. There is a Mutalisk and a Guardian hanging around an Extractor that will need to be killed. Destroy the Extractor. Broodling any Ultralisk that is visible. Move up wave after wave of Zerglings and Hydralisks and Ultralisks into the Zerg base, and change the rally points of the Hatcheries to be in an appropriate place within the Zerg base. The Terran usually do not assist in the defense of the Zerg base, which is good. If you are quick enough, there may be some minerals/gas left in the Zerg base.
If you have made it this far, it is a simple thing to destroy the Terran base. There is a group of Sunken Colonies and Spore Colonies along the northeast edge of the Terran base. Destroy the first ones in the north. Build a Nydus Canal in the original base, and place the exit in the area vacated by the Sunken Colonies. (You may need to destroy one or two Guardians to accomplish this.) Then set the rally point for each of the Hatcheries in the main base on the Nydus Canal. Forces will quickly appear on the edge of the Terran base where you need them. Broodling any Siege Tank or attack them at close range with Zerglings in order to enable the attack to move quickly. Destroy everything. Be creative. A group of 16 Ultralisks is very efficient at destroying all ground level units and structures. Or use Zerglings to destroy all buildings and ignore the air and ground forces. Or use Hydralisks to destroy all air units. Lots of possibilities.