This mission is a noticeable step up in difficulty from all of the previous Zerg missions in this campaign. Part of this, of course, is due to this mission's special handicap: you are not permitted to build a Spire (meaning no offensive air units), and you can not research the Overlord's Ventral Sacs transportation upgrades (meaning no drops). You are apt to notice this handicap when, during the mission, you face the daunting prospect of trying to take a ridge guarded by 4-6 reavers, or when trying to get across the bridge to the far bottom left corner against a seemingly endless tide of zealots, dragoons, dark templar, and dark archons clogging the way.
More fundamentally, though, this is the first mission in the Zerg campaign where you have to fight against the full fury of the Brood War Protoss - and you essentially spend much of the mission on the defensive through no choice of your own. The Computer's main base is on a giant island in the middle of the map that you can't touch, and they take full advantage of that. Expect dark templar attacks from early on in the mission, building and building until they come at you in groups of 10-12 with dragoons, zealots, and reavers for backup to tear apart your carefully placed sunken colonies. Expect Dark Archons to mind control your overlords and queens if you even give them half a chance. Perhaps most annoyingly of all, expect small groups of both carriers and reavers - and watch as they get recalled back to the main base on the verge of their destruction.
Fortunately, in spite of the handicap, you start off in a strong position, with a base that is naturally defensible (it is surrounded on all three sides (the fourth is to the edge of the map) with buildable ridges accessible from the ground, and all of which have plentiful resources. What you first need to do is start setting up defenses quickly. Place a few sunken and spore colonies near the two entrances to your Main Base, but don't go overboard - your primary defensive network will be built on the ridges. Get your resources flowing as quickly as possible, too, with two drones each to a mineral patch. Expect small attacks as this point, building into larger ones, so start building some hydralisks to supplement your defenses, and get their upgrades going. Make sure, through the next steps, to keep up with the upgrades - even small edges make a difference in this mission.
Once the resource situation has been set up, get a small force of your guys with an overlord or two (hopefully upgraded for speed), and expand to either the top or right ridge first, building your hatchery. Keep the hydralisks up there for security until the hatchery is finished, workers are mining the resources (if you went for the right ridge), and you have at least 6-7 spore colonies on the right ridge around your hatchery, with 3-4 sunken colonies near the ramp. The right ridge will take the brunt of the enemy's major air assaults for most of the game, so it needs to be as defensible against them as possible (remember the golden rule of Zerg defensive structures: they are more effective when clumped together, particularly if your opponent isn't terran). Remember to make sure, though, that you keep your spore colonies close enough to your sunken colonies to provide detection against the numerous dark templar attacks.
Follow this by expanding to the top ridge (or middle ridge with no resources) next. Try to get the sunken colonies as close to the edge as possible; one of the key purposes of this cliff based defense is so your sunken colonies can attack the reavers that frequently wander by on their way to one of the two major entrances to your base without getting attacked back. Five or six is the best, with as many spore colonies as you can fit behind them. Make sure you don't clump so tightly that replacement drones can't get in; you will probably be replacing both the sunken and spore colonies on the Middle Ridge a lot over this mission.
Finally, take the bottom (or left) ridge. It is the least secure, since its entrance faces outward from your base, so make sure to fortify it with plenty of sunken colonies near the ramp, interlocked with spore colonies. DO NOT FORGET to make sure that the spore colonies are close enough to the sunken colonies to provide detection; when I first tried this mission, I made this mistake, with the result that I lost a huge chunk of the defensive structures on the left ridge after the combined Dark Templar/Dragoon/Zealot attack killed the sunken colonies and then proceeded to work on the spore colonies.
Once you have this massive defensive network in place, the sunken colonies on the ridge should interlock with the earliest ones on the ground to either stop or greatly slow ground attacks into your main base while minimizing casualties.
Feeling nice and snug after completing the above? Good, because now begins the hardest part of this mission: actually assaulting the bloody platforms. I strongly suggest, through the next part of this mission, that you save, so that if something goes wrong you can try a different approach. On the bright side, you now have enough resources to last you a long way, although it may not be enough to finish the mission with unless you are very skilled at micro-management - the attrition, in terms of units and defensive structures, of this mission is very severe.
You should have at least five hatcheries at this point, with one of them being your central Hive. Build a sixth one, so that you can build at least 18 units at once. Once this is in place, continue with the upgrades, and build some Queens; they are crucial to your scouting on this mission. I strongly recommend that you win this mission with a combination of zerglings, hydralisks, and lurkers. You can try ultralisks, but be extremely cautious; like overlords and queens, ultralisks are high-value targets that will be the first to be Mind-Controlled by the ubiquitous Dark Archons around this map.
I would recommend sending at least 24 hydralisks (36 is better, but more unwieldy) along with 8-10 lurkers for the first platform northwest of your middle ridge. The lurkers are extremely valuable as long as you keep them out of the sight of detection; they are devastating to ground units, and can provide "cover fire" for your hydralisks and Duran as you retreat them from the platform after getting Duran to the Beacon. Once your parasites are in place (and any high templar are spawn brooded), move your hydralisk up the platform at once. Don't stop until they are all up there, even though you may take casualties - you will take more if they simply clog the ramp to shoot at targets. Bring the lurkers up with them, even if you haven't killed the photon cannons; expect the Computer to drop guys to retake the platform. Run Duran cloaked up to the beacon once the cannons are dead, then as soon as he is finished, get him off the platform, along with the rest of your forces, and bee-line straight back to your base. As mentioned earlier, the attrition rate for your forces in this mission is severe, so you need to conserve them as much as possible.
Let Duran regenerate his cloak, but at the same time, start moving your forces up to the open area just east of the second platform (which is directly north of the right ridge in your main base). While Duran is healing, send in your Queens to Parasite and Spawn Brood High Templar, then start some hit and run. Set up your lurkers at the bottom of the ramp, then bring up 12 hydralisks to kill any cannons near the top of the ramp. When the protoss retaliate, run back down the ramp, and let your lurkers chew up the counter-attack. If you want to take this one step further, then once the cannons near the ramp are destroyed, move your lurkers up to the top of the ramp, and position them there; they'll give you cover for your 36 hydralisk force to get up and start attacking. Follow the same pattern as the last platform - kill any attacking units and the photon cannons, but mainly focus on getting Duran to the Beacon and back as fast as possible.
To BE CONTINUED . . .