But what exactly is it that you can't do? I agree with him, you just can't do BW muta micro in SC2. This is just to supplement Decency's answer (below) for readers who are unfamiliar with Brood War please read it first. Jaedong does it easily, like this game, and routinely wins because of it. Mutalisks that are microed well can kill Scourge (flying single-target suicide bombs) but it's ridiculously hard to do, especially during a battle. Nearly every game in this matchup in SC:BW became a micro heavy battle between Zerglings, Mutalisks and Scourge for each player. The matchup is frequently referred to as JvZ. Zerg, which Jaedong at one point had an absurd 80% career winrate in. There's no corner or high ground area for him to sit in while he macros, he has to do it on the fly.ДЄfter typing all that I realize that he also might be talking about Zerg vs. As you can see, once Jaedong enters the base he is CONSTANTLY forced to micro his Mutalisks until he departs, and departing causes him to take exit damage. How well he does this determines how much damage he takes. After the attack projectile flies, he immediately pulls back to minimize damage. Jaedong is engaging and frequently targeting specific out of place units. Two-group micro starts a few minutes later, at 11:30. This (incredibly difficult) technique allowed him to do things no other player was capable of and unlike most players who built an initial wave of Mutalisks and used them to deal as much damage as possible until they died, Jaedong often strengthened his air army as the game went on and won with it.

Jaedong was the first to micro two control groups of Mutalisks at the first time effectively while still macroing well. This was changed in SC2 for no apparent reason, making tactical maneuvering of Mutalisks unimpressively dumbed down.

Because of this, Mutalisks could be microed from fog of war to deal huge damage.

A final mechanic that leads to effective Mutalisk harass is that in Brood War, air units that attack from high ground don't reveal themselves and thus can't be attacked.

In SC2, units are frequently just clumped into an impenetrable ball.

Because pathing isn't very good, ground units are occasionally out of place and can be eliminated.

The typical way to accomplish this is by selecting 11 Mutalisks in addition to a pinned-in Zergling, an overlord, or a larva. In the case of flying air units like Mutalisks, this means that they will stack on top of each other and can effectively be microed like a single unit. If any single selected unit is outside of this box, the units will each try to execute the same command.

When units are given a command, they will move in a formation if all of the selected units are within what's called a 'magic box' (the original use for the term).

SC2 is played with a minimum latency of ~200ms, making controlling units with exacting precision essentially impossible.

StarCraft 1 is played professionally with a latency of only a few milliseconds.

Mutalisk micro in StarCraft 1 is made versatile because of the mechanics of the game: Again, Brood War has soft counters, not hard counters. Turrets are also cheaper, but only deal half damage (10 of 20, instead of SC2's flat 24) to Mutalisks and so can be fought around more easily. Your units can thus be cut off by Marines much more easily and must be constantly looked after. However, few maps in have areas near bases where you can hide your Mutalisks risk-free. When repeating this, it's possible to open up an opponent with your harass and force him to spread units so that you can take advantage of weak points in his defense. In Brood War, Mutalisks can actually engage Marine groups and kill the outside ones without taking enormous amounts of damage. Stimmed Marines can nearly catch them, but they only have 40 health and start with 4 range instead of 5. In StarCraft 1, Mutalisks are not very fast and have a smaller range. In general, 'counters' in Brood War are much less definitive than they are in SC2, and there's no exception here.

Starcraft 1 control groups