Pre-3.8 StarCraft History
Throughout nearly all of StarCraft 2 Mutalisks have been the go to tier 2 tech in the Zerg vs Terran match-up. Ling, bane muta was a popular composition that had a lot of mobility for defending as well as power in their ability to counter attack and deal harassment damage. The Hydralisks was torn apart by opposing Terran bio armies, they were squishy and couldn’t survive long enough to deal more damage than Mutalisks would have. This combined with the fact that they had poor mobility, had crucial upgrade(s) that delayed their usefulness and couldn’t be used for harassment nearly as effectively meant that the Mutalisk ruled the ZvT Matchup.
However all of that is almost exclusive to pre-patch 3.11. So what did blizzard change that increased their usefulness in the match-up?
It is clear that these two changes allowed the Hydralisk to go from being a joke of its Brood War self to being a powerful tool Zergs could use in the match-up.
GSL Code S Ro.32 Scarlett vs INnoVation Game 1 Abyssal Reef
SSL Premier Season 1 Finals Solar vs INnoVation Game 1 Frost
These two games showcase the beginnings of Zergs Transition to Hydra based armies. We can see that mutas weren’t working as well as they used to either:
SSL Premier Season 1 Finals Solar vs INnoVation Game 3 Abyssal Reef
SSL Premier Season 1 INnoVation vs ByuL Game 2 Abyssal Reef
This last game showcases perfectly the positives and negatives of mutalisks in the match-up. ByuL is able to get a lot of damage done to INnoVation with Lings and Mutas, however because INnoVation’s bio army with widow-mine support just grows in size and the mutas can’t do anything in a head on engagement, INnoVation can just walk across the map and kill ByuL.
The Terran Army
One big factor to consider when considering hydralisks and mutalisks is the Terran army composition. The most common Terran army to ling bane muta is a marine, medivac, widow mine based army. On the contrary, the Terran army changes to marine, medivac, siege tank when playing against ling bane hydra.
Why does this change occur?
Groups of widow mines have the ability to kill large clumps of mutalisks while at the same time single widow mines have the power to kill large amounts of ling bane if the zerg player is not careful. They are powerful zoning tools that increase the power of the Terran pushes. However hydralisks out range widow mines with the muscular augments upgrade and don’t clump together nearly as much as mutalisks. This means Terrans are switching to siege tank tech to deal with the hydras, allowing ling bane armies much more freedom to engage fully against Terran pushes.
Additionally, the Thor was recently changed to have 2 base armor instead of 1. This makes them harder to kill for zerglings. Their powerful anti-air splash attack allowed Terran to build 1-2 Thors in the mid-late game against a ling bane muta player and they could eliminate any mutalisk flock that attempted to attack a pushing Terran army or defend muta flocks that were trying to get harass damage done.
Simply stated, Terrans have many different powerful answers to mutalisks in the match-up, while their answer to hydralisks is not nearly as good.
Hydralisks cost 50 gas. Mutalisks cost 100 gas. Ultralisks and hive tech are important for swinging the game into Zergs favor and banelings are important for defending early Terran attacks. Banelings, Ultralisks, Infestation pit, Hive and important upgrades (centrifugal hooks, chitenous plating, adrenal glands etc) all cost a lot of gas.
When your tier 2 tech option costs 50% less gas, you can tech much faster and afford more banelings. You can also take gases later allowing you to drone faster and get more queens and Zerglings.
Mutalisks are not in a good position in the meta right now. They have little use in head on engagements and Terrans have a plethora of ways of dealing with them. This combined with the fact that they cost twice as much gas as their main competitor, the hydralisk has basically omitted the mutalisk from the current meta (at least at professional levels).
In comparison, Hydralisks have recently gotten buffs that allow them to defend easier with more mobility and fight better with a health buff. They cost less gas which makes it easier to get to important tech such as ultralisks in the lategame.