Minecraft – How to earn the ‘Sniper Duel’ achievement in Minecraft

Build a refinery first, then add a bunker next to each of the existing ones by the bridges. Build a billion SCV's , a billion supply depots, and 4 barracks (one with tech and 3 with reactors). Tech barrack should only produce medics other three should only produce marines. Don't worry about stranded rebels, keep all troops near bunkers until about 9 minutes are left. Attack the Zerg base at the top left of the map with a force of about 30 marines. concentrate fire on Zerg troops until there are none then have half the marines fire at each hatchery. THE MOMENT you have destroyed BOTH hatcheries, immediately pull your troops out into the corner away from the Zerg base, do not destroy anything further. Keep building troops and after a few minutes send a second force of roughly 20 or so troops to meet up with the first force. The hatcheries should have respawned by now and you can go in and destroy them both with little resistence a second time to earn the achievement.

Here's a helpful link with a full description:

http://wiki.teamliquid.net/starcraft2/Campaign/Media_Blitz

Strategy summarized from the above link:

During the surprise attack, start with the mech-base destroying all siege tanks and factories. Use the remaining time to destroy as much of the starport base as possible.

After the surprise attack, immediately send the Odin, initial Thor, and 2 repair SCVs to attack the 2 bases closest to your own base. Concurrently, produce two more Thors and an armory to research vehicle upgrades.

Right after the two small bases are destroyed, take out the starport base, the mech base, and finally the infantry base.

Continue to produce & deploy Thors and repair SCVs throughout the mission.