[ES] Unit Composition and Utility

This is the seventh entry of The Elementary Series.

There are many units in the game, and this often overwhelms newer players. This article discusses the basics of unit composition and utility.


We always hear people say, “macro better”. Sure, the more you have the better it is. But what units you have is equally important. Fundamentally, it is about understanding the utility of units. Some units do better in something than other units. Having units to fit different roles is an integral part of Starcraft II game design. Blizzard have a history of tuning units when units are used in ways that are not in line with the intended ways.

The main purpose of this article is to help newer players understand unit composition better by breaking it in a systematic way. Newer players often find it extremely challenging to know what units to produce. It is difficult to learn from the pro-players when they appear to produce all sort of units and mix them together somehow. Take a look at the screenshot below for an example. It is a game from the GSL Final between Maru and TY. It is a mirror match, and the unit tab shows that there are Reaper, Marine, Hellion, Cyclone, Widow Mine, Siege Tank, Viking, Banshee, and Raven. How can we expect the newer players to understand this mess systematically and apply it to their own games?

 This article first discusses the formation of a basic composition by breaking it down into different parts. Then, it takes a step back to discuss how the utilities of units influence when certain units are used, and in turn influence their inclusion in a composition.

Forming a composition

Core units

The basics of unit composition are best understood by studying the mid game. Players tend to produce different units in small numbers in the early game, and this has a lot to do with the build order choice. No matter what they build in the early game, they tend to converge to a mid game composition that is made up of several core units.

Core units generally:

  • complement each other;
  • are versatile; and
  • allow other units to be mixed in to enhance effectiveness

For example, Marine and Medivac are the core units of a bio composition. Every bio composition variation always consists these two units. Marine’s  Stim and Medivac’s heal complement each other extremely well, and this combo is even mentioned in the load screen tips. Marine and Medivac are versatile in the sense that they can be used in most situations. Being versatile does not mean that the composition cannot be more effective by mixing in other units to counter opponent’s opposition. This leads to the next point.

Supplementary units

Supplementary units are mixed in with the core units to optimise the effectiveness of the composition. Using the same example, Marauder and Siege Tank are often used to supplement Marine and Medivac. Marauder is added in TvP, while Siege Tank is added in TvT.

Marauder is essentially a “specialist” Marine, as it has Stim and the same mobility as Marine. Marauder is more effective than Marine against armored units (e.g., Stalker), and its Concussive Shell makes engagement more favourable. Marauder also provides much needed “muscle” for the Marine.  Then, why isn’t Marauder considered a core unit? This is because Marauder has a lower dps than Marine against non-armored units. This is best demonstrated in TvT, whereby players use Siege Tank instead of Marauder as the supplementary unit. Marine beats Marauder, so Marauder is simply inferior in a bio mirror battle. Although Marauder is theoretically better than Marine in dealing with Siege Tank, it is difficult for Marauder to have the opportunity to attack Siege Tank in game. If they do, they have to get past the Marine, and Marauder does not beat Marine.

Let’s use another example. Zergling and Baneling are the core units, but they have some limitations such as not being able to attack air units. Hydralisk, Roach, and Mutalisk are some options of supplementary units.

The composition of core and supplementary units can be decided before the game starts, because you know what supplementary units should be selected in that specific match up.

Support units

Support units can be added into a composition for two reasons:

  • Counter opponent’s composition
  • Specific strategic or tactical considerations

While your main composition is considerably all-rounded, it is important to mix in specific units to counter opponent’s composition. For example, in TvZ, Terran would mix in Thor as a response to Zerg’s Zergling, Baneling, and Mutalisk composition. Thor is a good counter to Mutalisk. Conversely, Zerg would mix in Viper to counter Terran’s Siege Tank heavy composition. It is important to note that these support units are only constructed because opponents make certain units.

Support units can also constructed for specific strategic or tactical considerations. For example,  Liberator is produced in TvZ mid game for harassment reasons. Liberator is a good option to harass opponent’s mineral line, because it stretches opponent’s attention more than yours. Liberator harassment usually occurs when Terran make a push with their main army toward Zerg’s most vulnerable base. It is difficult for Zerg to allocate attention to your main push and deal with the Liberator at the mineral lines elsewhere. Importantly, Liberator is not produced in the mid game to counter Zerg’s composition, but it is used to gain an advantage tactically.

The above discussion provides the foundation for understanding the formation of a composition. Next, I will breakdown additional factors that drive certain units to be used in specific time.

Unit utility in game stages

Some units are produced only in certain stages of the game. Reaper is the perfect example, as it is only produced in the early game. This is because, the utility of Reaper is mainly limited to scouting in early game when there are few units.

I am not going to list out when to use each unit for each match up, as that is not practical. More importantly, I believe it is better to understand the underlying reasons than memorise the utility of each unit. Blizzard can always redesign a unit, so it is more educational and practical this way.

There are three criteria that decide why a unit is used at certain stages of the game:

  • Requirements
  • Scaling
  • Strategy


Zerg have a clear requirement as to when a unit can be produced. It is obvious that Ultralisk and Broodlord are late game units, because they require Hive. Unlike Zerg, Protoss and Terran can access to tech units by putting down the required tech building early on. This also explains why 1-1-1 is such a difficult build to use for newer players, because almost every unit is accessible early on.

Some units require other units to be effective. Viper, High Templar, and Raven are some examples. Viper’s Blinding Cloud and Abduct require other units to capitalise on the advantages provided. Hence, some units are only produced in later stage of the game because they require other units to be produced first.

Some units are only effective when they reach a certain number. Tempest is an example of such unit as it does not affect the battle field if there is only one. In order to produce a sizable number of Tempest, Protoss need to have a healthy economy. Thus, resource requirement can also push a unit to be produced only in the late game.


Some units scale better than others. Some units get better as the game proceeds, while others get worse. Units that do not scale well are usually not used as the game proceeds to the mid game.

Cyclone is a good example. It is so strong in the early game that it defines how the early game is played in the Terran mirror match up. While no other unit can rival Cyclone’s strength in the early game, it does not scale well. Once the game proceeds to the mid game with Stim research completed, Cyclone cannot compete with the Marine Tank army. Thus, we do not see Cyclone being produced in the mid game.


There are strategies that are effective only at specific timing, and units required for these strategies are produced in that time frame. Dark Templar is a good example. Dark Templar is best used at a time when the opponent does not have detection. Given that static defence is a bigger investment in the early game than in the late game, Dark Templar is considerably effective in the early game.

Raven is an interesting case. It is produced in the early and late game, but not in mid game, for strategic reasons. Raven can be produced in the early game for defence, and then used as a support unit for a timing push in the mid game. This is most commonly used in TvT, whereby Raven is first used in the early game against Banshee. It saves up energy for Interference Matrix, which is used in the mid game push against defensive Siege Tank. See below vod for an example.

Raven is also used in the late game to combo with other late game units. For the first half of 2018, Raven and Ghost form an effective composition in the late game against Zerg, and it is the main strategy in TvZ at that time. Raven’s Anti-Armor Missile is spammed on Zerg’s army when they try to interrupt Ghost’s Steady Targeting ability. See below vod for an example.


In sum, for newer players, it is beneficial to first decide your composition that is made up of core and supplementary units for each match up. This gives you a clear direction as to what to transition to from the early game and what to produce in the mid game. Subsequently, you can look at your notes to mix in specific counter units toward opponent’s composition. Understanding how requirements, scaling, and strategy shape the usage of units advances one’s knowledge as to why certain units are limited to specific timings and roles.

The next Elementary Series article discusses build order.

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2 thoughts on “[ES] Unit Composition and Utility

  1. >Blizzard have a history of tuning units when units are used in ways that are not in line with the intended ways.

    Why is this the case?

    If the unit gets too OP I can understand, but if the unit is not used in the intended ways isn’t it called creativity?

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