Heart of the Swarm Campaign- Char Achievements: Fire in the Sky

Normal Difficulty:

Fire in the Sky (10): Win.

Red Alert (10): Win with less than five units having died to Gorgon bombardment.  With a little patience, this achievement is simplicity itself.  There is essentially no reason to have multiple forces out of your base at once, you need no external buildings aside from creep tumors, and while the Gorgon attack zone is tremendous, the ships all fly a straight line across the map in the very center from right to left.  Since the scourge nests are almost all off of this line as well, you don't even need to worry about your creep tumors most of the time, and with the aid of queens to spawn additional tumors you should be spreading your creep quickly enough that you have access to scourge nests before you even need them.  Since this doesn't even count units that die to Warfield's airdrops or defenders, and the Gorgon won't fire on creep tumors, you are actually at very low risk of failing this achievement.

Conquer & Command (10): Destroy 3 Orbital Command Structures during the mission.  This is a little harder.  You have to invest time and troops into destroying the Terran bases in order to accomplish the third command center kill you need here, and you need to clear out nearly all of them to boot.  There are a total of four Terran command centers that you can reach on foot, so complete enemy destruction will give you even more than you need, but the time and focus it takes away can leave you with a hard challenge trying to get all the scourge nests in time.  Your best bet is to have one large attack force and run down each side-route as you reveal the entrance to it, so that you will always have the firepower on hand to get each job done quickly.

Hard Difficulty:

Going, Going, Gorgon! (10): Destroy four Gorgons within the first 2 minutes of the mission.  This is a serious rush to try and pull off.  If you're going to manage it, a strong investment in zerglings is pretty much mandatory- you'll need to gather resource crates as opportunities strike and otherwise aim straight for the scourge nests- even ignoring the need to increase your resource income.  Move-speed boosts and the pouncing zergling variant are an absolute necessity to accomplish this, as are a quick hand with Kerrigan's abilities and just enough investment in improving your vespene gathering to throw out multiple queens.  Banelings become wasteful in such a situation, so focus entirely on having a high zergling output and increasing offensive capability until the four battlecruisers are down- once this is accomplished, though, you'll need to step back your offense and quickly ramp up your income so you can use heavier units.  Otherwise you're going to be wielding an easily-crushed zergling-queen force against a rather large number of Terran attacks and the deadly splash of siege tanks.