This mission can be easier than you might expect, being the next-to-last mission for the Zerg. The only real challenging part comes after you've reached the crystal and must survive for ten minutes. Fortunately, the Protoss don't come in hordes at your at that time. First, build twelve drones to harvest minerals. After that, build another hatchery just south of the vespene geyser. Your unit production will be doubled and you'll be able to harvest gas easier. Since you started with plenty of gas you should work on upgrades. I highly recommend you pick carapace. One thing I don't usually recommend will come into play on this mission. Build plenty of static defenses. Not a lot, but make sure your base is well covered by both sunken and spore colonies. The spores are highly important as the Protoss can build the fearsome carrier in this mission and will surely use it against you.

To begin going on the offensve you should first have climbed up the tech tree. The Protoss, as always, have those annoying reavers which can really mess up a ground assault. Get six guardians, 24 zerglings and eight hydralisks. Use some scourge to scout out the protoss base dead east of yours (ground forces have to go north around the land formation). The purpose of this is to spot reavers. When you're ready to begin the attack, move your ground troops out of sight range of the enemy base. Now close in with your guardians and knock out those damned reavers, but don't make it a suicide run. Shoot down any anti-air capability your enemy has first, just don't bother shooting every photon cannon. Target anything that can hurt your guardians. Zerglings are expendable and perform quite fine at taking out photon cannons.

When the reavers are gone, move in with your other troops. The guardians can provide cover fire, shooting at zealots and moving about scouting for reavers. If any air units attack you quickly order your hydralisks to attack! Before too long, the area will be secure. This is a great spot for an expansion base.

When the hatchery's done, build up some more static defenses on the southern side of your new base. Get drones working here to speed up your resource allocation. Look to the northeast of the conquered protoss base to see another great spot to set up an expansion. You'll have a total of four hatcheries and three vespene geysers. This will make this mission even easier.

Back at your main base it would be wise to build a few scourge to use should a carrier attack. They might be able to soften it up significantly for your spore colonies to deliver the finishing blow. Another thing you can do now is build ultralisks. I didn't recommend them in the first battle because they weren't really necessary, but you can really use them now! Replenish your forces to mimic the last group only make it much larger (12 hydralisks instead of 8, maybe even 36 zerglings instead of 24), and with at least four ultralisks to help!

Before you go for the gold, I recommend taking down another Protoss base. This one is southeast of the base you just destroyed. Prior to leaving for this assault, make some extra units at each base to protect it. Hydralisks and zerglings will be very useful to you, but you might want a few mutalisks hotkeyed to attack any reavers that assault your base while your primary force is out mopping up the map. Do just like before with the next assault. Lead with some scourge to learn the layout of the enemy base then smash into him with your guardians while your ground forces wait for the right moment.

You should now be safe to send a drone in to harvest the crystal. Destroy the few Protoss that are guarding it, then make the drone enter the beacon. A ten minute countdown will ensue, and with the Protoss down to the base to the southwest, you should be able to stave off their attacks. If carriers attack you, which are by far the most threatening thing (other than reavers) you should use a few scourge to destroy it. Four can take one down in a single swoop. When the ten minute countdown is up, you can send the drone back to the beacon at your base. When it reaches it, you're victorious.