One of the unique features of the Starcraft 2 Heart of the
Swarm campaign is the introduction of the Evolution Pit and the Evolution Missions. The Evolution Pit offers
players the opportunity to augment key Zerg units, making them much more powerful. The Zergling, Baneling,
Roach, Hydralisk, Mutalisk, Swarm Host, and Ultralisk can all be eventually modified in the Evolution Pit.
There are two ways to augment units in the Evolution Pit: via Mutation Upgrades and via Evolution Strain
Mutation Upgrades are available as soon as a particular unit is unlocked and can be
changed at any time from mission to mission.
Evolution Strains are unlocked by playing the "Evolution Missions", which when unlocked
can be accessed from the Evolution Pit. Players have to choose between two possible evolutions for their
particular unit. These choices are permanent and cannot be changed until you have played through the entire
Heart of the Swarm campaign (you can change in the Master Archives).
Below, you will find a video guide discussing the best upgrades as well as a text list that includes
descriptions of all the mutations and evolutions as well as a guide to the best combinations of mutations
and evolutions available to your units in Heart of the Swarm.
Evolution Pit Video Guide
Zergling Evolution and Mutation Upgrades Guide
Zergling Mutation Upgrades
Hardened Carapace - Zerglings gain +10 life. This is actually a very good choice if you
are using Splitter Banelings with healing (discussed below). Between this healing and Mend, Zerglings actually
can live a long time and deal large amounts of damage before going down.
Adrenal Overload - Zergling attack speed increases by 50%. This is a huge increase in
damage per second, and the de facto choice for Zergling Mutation.
Metabolic Boost - Zergling movement speed increases by 60%. Normally, this upgrade is
really good, because the movement speed significantly increases Zergling uptime on a target. However, the
Raptor strain takes care of this, so I do not recommend this mutation.
Zergling Evolution Strains
Raptor - Allows the Zergling to leap up and down cliffs. Also, when Zerglings get near
their target, they leap to the target, closing distance almost instantly. Zerglings also gain +2 damage per
Swarmling - Zerglings spawn in groups of 3 and morph nearly instantly.
Recommended Zergling Evolution and Mutations
When it comes to the Raptor and Swarmling, I think that the Raptor wins, no contest. Zerglings are so fragile in
the Heart of the Swarm campaign because you are always attacking fortified positions. The computer always has a lot
of Bunkers, Siege Tanks, and Hellbats in position to roast your Zerglings alive. Zerglings are so effective in
multiplayer play when they surround armies in the open field - they are horrible at directly attacking fortified
positions due to their low HP count.
For this reason, you have to pick the Raptor. The Raptor can leap to its targets, giving it a lot more uptime on
its targets. The +2 damage is an unexpected but very nice bonus as well.
For the Mutation strain, you can either go with Adrenal Overload or Hardened Carapace. On paper, Adrenal
Overload looks best. However, as mentioned, since you are constantly attacking fortified positions in Heart of the
Swarm, sometimes the extra health will double or triple a Zergling's life expectancy, particularly if you use Mend
regularly with Kerrigan or Queens are around to heal your units.
I do not care for Metabolic Boost with the Raptor upgrade. It is redundant given that the Raptor already can
leap to enemy targets.
Baneling Evolution and Mutation Upgrades Guide
Baneling Mutation Upgrades
Corrosive Acid - Banelings deal 100% to the primary target. Splash damage remains the
same. This is my preferred upgrade with Hunter Banelings, as you can use the leap to sneak down important
targets to end missions early.
Rupture - Blast Radius increased by 50%. While this mutation can be good if you are
planning on massing Banelings for offense, for the most part I do not find this is an efficient way to play the
later missions due to too many Siege Tanks and air units..
Regenerative Acid - In addition to dealing damage to enemy units, friendly units and
structures within the Baneling's area of effect are healed by the explosion. This works much better if you have
Splitter Banelings, particularly if you use Zerglings or other melee units with the Banelings. It does not work
well with Hunter Banelings, as the Hunter Banelings will jump ahead of your melee units too frequently.
Zergling Evolution Strains
Splitter - Upon death, the Baneling splits into two smaller Banelings that can also
explode (but deal less damage). Works well with Regenerative Acid, as the large number of explosions dishes out
a lot of healing.
Hunter - Allows the Baneling to jump up and down cliffs. The Baneling can also leap
to its target, jumping over enemy units to hit the preferred target.
Recommended Baneling Evolution and Mutations
There are two strong options for Baneling play in the Heart of the Swarm Campaign. I prefer to get Hunter
Banelings with the Corrosive Acid upgrade. This gives you a mobile, targeted, high-damage Baneling that you can use
to cheese your way through a few missions in a short amount of time.
Any mission that simply relies on you taking out a particular structure can be ended early by massing up Hunter
Banelings with Corrosive Acid, approaching the target from the least defended side, and rushing in to blow it up.
This can help unlock some of the tougher Mastery achievement timers.
The other good option for Banelings is using the Splitter Banelings with the Regenerative Acid option. This
works well if you like to use mostly melee ground units like Zerglings, Abominations, and Ultralisks (which will
actually be in range to be healed) as well as if you like to use Banelings as part of your main army.
Personally, I find that while this combination works, it is not as cost effective as I would like, so I tend to
stay away from it. It does make for a fun alternative method of play though.
Roach Evolution and Mutation Upgrades Guide
Roach Mutation Upgrades
Hydriodic Bile - Roaches gain +8 damage versus light units.
Adaptive Plating - The Roach gains +3 armor when under 50% health.
Tunneling Claws - The Roach can move at full speed when burrowed. Life regeneration rate
increased by 100% when burrowed.
Roach Evolution Strains
Corpser - The Roach's attack will debuff the enemy for a few seconds. If the any dies
while the debuff is active, two "Roachlings" will spawn from its Corpse. These are timed units that are similar
Vile - Vile Roaches debuff enemy targets with their attack, reducing enemy movement
and attack speeds by 75%.
Recommended Roach Evolution and Mutations
There is one Roach combination that is significantly better than all the other choices, and that is the Vile
Roach with the Hydriodic Bile upgrade. The Splitter Roach is just not very good. Roaches die too easily to
high-powered units like Thors and Siege Tanks. Vile Roaches reduce the damage by so much and are in all ways
superior to the weak Roachlings that spawn from the Corpser Roaches.
For mutations, Hydriodic Bile is the best since it directly boosts Roach DPS. Adaptive Plating might work well
in the first few missions, but as soon as you start running into heavy Thor and Siege Tank armies, this upgrade is
not very noticeable. Tunneling Claws does not work well since you are almost always assaulting fortified positions
where detection is everywhere.
Hydralisk Evolution and Mutation Upgrades Guide
Hydralisk Mutation Upgrades
Frenzy - Gives the Hydralisk the "Frenzy" ability, which increases attack speed by 50% for
15 seconds. This has a 30 second cooldown.
Ancillary Carapace - Increases the Hydralisk's maximum health by 20.
Grooved Spines - Increases the Hydralisk's range by 1 from 5 to 6.
Hydralisk Evolution Strains
Impaler - Allows the Hydralisk to morph into an Impaler. The Impaler can only attack
while burrowed. The Impaler has a long range (11), attacks targets one at a time, and deals bonus damage to
Lurker - Allows the Hydralisk to morph into a Lurker. The Lurker also attacks
while burrowed. The Lurker has a shorter range (6), attacks targets in an AoE-cone, and deals bonus damage to
Note that the Hydralisk Evolution Strains do not prevent you from accessing the Hydralisk. Instead, you can
morph your Hydralisks into these units if you choose for an additional resource and supply investment. You can have
both Hydralisks and Impalers/Lurkers in the same mission.
Recommended Hydralisk Evolution and Mutations
There are two options for the Hydralisk. Frenzy is probably the best upgrade, but only if you can remember to
activate it. In later missions, you likely will be focusing all your microing efforts on Kerrigan and the
Leviathan, so you will not have the luxury of babysitting this ability. When this becomes a problem, switch over to
The other choice you have to make is the Impaler versus the Lurker. The Lurker has a short range, bonus damage
to light units, and an AoE attack. The Impaler has a long range, bonus damage to armored units, and a single-target
I find the Impaler to be the superior unit. The Impaler is both an offensive and defensive unit, while the
Lurker's range is too low to safely use it on offense. The Impaler deals bonus damage to armored units (which
includes structures) and has a long range, so it is great at attacking heavily fortified Terran encampments on
offense. The Impaler is also great on defense against mech attacks. Thor-based ground attacks are particularly
devastating, and the Impaler handles them with ease. The Lurker cannot deal with Thors nearly as easily.
The Lurker is strong versus Infantry attacks, which are just not that dangerous in the first place. I've never
had to pull Kerrigan back for defense against Marines. I have had to pull her back to handle Thors though!
Mutalisk Evolution and Mutation Upgrades Guide
Mutalisk Mutation Upgrades
Vicious Glave - Mutalisk attacks bounce 3 more times and each bounce does more damage and
travels farther than normal.
Rapid Regeneration - Mutalisks rapidly regenerate their health outside of combat. This
does require the Mutalisk to sit out of the fight for 5 seconds.
Sundering Glave - Mutalisks deal +9 (double damage) to armored targets. Mutalisk attacks
no longer bounce.
Mutalisk Evolution Strains
Brood Lord - The Brood Lord is a long-range air unit which spawns
Broodlings each time it attacks. Broodlings are short-lived ground units with a fast melee attack and a low
amount of HP.
Viper - The Viper is a flying support unit with a variety of abilities. It can pull units
to it as well as cast a cloud which prevents enemy units and structures from attacking.
Recommended Mutalisk Evolution and Mutations
When it comes to picking between the Brood Lord and the Viper, you have to go with the Brood Lord. This is
the most important choice you will make in the Heart of the Swarm Campaign. It is not as if the Viper is bad,
but it is hard to use, because your attention should be focused on controlling Kerrigan, the Leviathan, and
macroing up. Manually controlling Vipers is slow and inefficient.
The Brood Lord on the other hand is the best supporting unit you can use in the Heart of the Swarm campaign.
Brood Lords are devastating as it is in multiplayer, but they are kept in-check by players who are able to manually
focus them down. The computer on the other hand does not have this level of intelligence, and instead will focus on
attacking whatever is in range. Since the Brood Lords have a long range, the Leviathan and the Broodlings will soak
up a lot of damage, while Kerrigan keeps everything healed up.
For the Mutalisk's mutation strains, you have to ask yourself what role the Mutalisk will play in your army. I
find the Mutalisk too expensive and too fragile to use on offense beyond the first few missions where it is
introduced. Instead, I like to use a small pack of Mutalisks to act as defense against enemy units.
In particular, Spine and Spore Crawlers tend to be weak versus Thors, Siege Tanks, Carriers, and Colossus. For
this reason, I really like Sundering Glave, which doubles the Mutalisk's damage versus armored targets. Whenever
you need to quickly reinforce an area that is getting hammered by Thors or powerful armored units, Mutalisks can
quickly fly there and burn those units down thanks to the Sundering Glave upgrade.
Vicious Glave represents the greatest DPS increase for the Mutalisk, but I feel the Mutalisk is too expensive
and fragile to use on offense in this manner, which is why I prefer Sundering Glave and a handful of Mutalisks for
defense. Rapid Regeneration is not my favorite since Kerrigan has Mend that can rapidly regenerate Mutalisk health
if you want healing, and Rapid Regeneration does not work in combat.
Swarm Host Evolution and Mutation Upgrades Guide
Swarm Host Mutation Upgrades
Burrow - The Swarm Host can now burrow, only being able to be attacked in the
presence of a detector. The Swarm Host can still spawn Locusts while burrowed. This is similar to the way the
Swarm Host functions in the multiplayer version of Heart of the Swarm.
Rapid Incubation - Increases the spawn rate of Locusts by 20%.
Pressurized Glands - Grants the Locust the ability to attack both air and ground
Swarm Host Evolution Strains
Carrion - The Swarm Host now produces flying Locusts. Flying Locusts are faster and
deal 50% more damage. They have 25% less life.
Creeper - Creeper Swarm Hosts generate Creep when burrowed. They can travel
quickly to any location where there is creep (they practically teleport). This teleport ability has a 10 second
Recommended Swarm Host Evolution and Mutations
For the Swarm Host's mutation upgrades, Pressurized Glands wins hands down. There are so many air units in Heart
of the Swarm that the Locust's ability to attack air units is essential to make the Swarm Host a viable unit. Rapid
Incubation does slightly increase the Swarm Host's DPS, but I find anti-air abilities to be more useful. Burrow on
the other hand is just a waste since there is so much detection in the campaign.
Choosing between the Carrion and Creeper is a similar story - the Carrion evolution is just a lot better. With
flying Locusts that deal 50% more damage, the Carrion can be used on offense in large numbers. This is a great
way to complete a mission in a cost-effective manner on a mission where you otherwise may be limited in resources,
such as the "Death From Above" mission.
The Creeper on the other hand is only really viable on defense. It is not a bad unit in theory, but the problem
is attention and micro. This unit does require attention and micro, whereas you really want to focus most of your
attention on controlling Kerrigan and the Leviathan.
Any time spent microing the Creeper around is time lost spent controlling Kerrigan or macroing up. If you do
want to try this unit however, make sure to use the Malignant Creep upgrade. The Locusts you produce with this unit
will practically always be on Creep, so you might as well boost their effectiveness by 30%.
Ultralisk Evolution and Mutation Upgrades Guide
Ultralisk Mutation Upgrades
Burrow Charge - When the Ultralisk gets close to its target, it burrows and charges it,
knocking back all nearby units and stunning them for 2 seconds. This ability has a 10 second cooldown. This
ability automatically casts.
Tissue Assimilation - Ultralisks gain life equal to 40% of all damage dealt from normal
attacks. Normal attacks means that it does not grant extra healing if you chose the "Noxious" variety of
Ultralisk in the Evolution.
Monarch Blades - Ultralisks deal 25 damage to all targets within range. Normally, an
Ultralisk deals 25 damage to its primary target and 5 damage in splash damage to nearby enemies. This causes
all enemies to take 25 damage.
Ultralisk Evolution Strains
Noxious - Gives the Ultralisk an aura which always deals 5 damage to nearby enemy
units. Also, the Ultralisk gains the Toxic Blast ability, which deals 20 damage in an area of effect to all
nearby enemy units and structures.
Torrasque - Ultralisks that die turn into a Chrysalis and are reborn a few seconds
later with full HP. This can only occur once per minute.
Recommended Ultralisk Evolution and Mutations
When comparing the Ultralisk Evolution Strains, the Torrasque wins, hands-down. It means the computer will have
to kill each Ultralisk you produce at least 2 times - perhaps more if you keep it alive long enough for the 60
second cooldown to reset. It allows your Ultralisks to absorb a ridiculous amount of damage while Kerrigan and the
Leviathan wreck the enemy's base.
With the Torrasque Ultralisk, I like to use Kerrigan with Mend and the Tissue Assimilation mutation upgrade.
This extra healing stretches out the Ultralisk's lifespan even further, making them practically impossible for the
computer to kill.
The other Mutations are pretty good for the Ultralisk as well. Burrow Charge is a solid choice, particularly for
Noxious Ultralisks, as the stunned units will take damage from the gas clouds. Burrow Charge also increases the
Ultralisk's survivability, as it prevents them from taking some hits from Siege Tanks. Monarch Blades on the other
hand represents a substantial DPS increase, so both work for the Noxious Ultralisk.
My preferred combination however is the Torrasque with Tissue Assimilation. This are as effective as Brood Lords
as part of your army, so if you did not pick Brood Lords, hopefully you grabbed Torrasque Ultralisks!