Zergling evolution

Zergling evolution is the first evolution mission available in StarCraft II: Heart of the Swarm.

Mission
Abathur located two mutations that could be used to permanently enhance the zergling breed. However, he advised that only one could be utilized, as the mutations would mutually compete within the zergling's genetic code. Sarah Kerrigan ordered some of either mutation be mutated for her to see how they fared in battle.

On the world of Calus, a Terran Dominion security outpost had been built on a mountainous area that made it difficult for ground forces to assault the base. Abathur's solution was to kill and assimilate members of the local karax population to gain their powerful leaping abilities. The zerglings in the area did so, mutating into the raptor strain. The raptors overwhelmed the Dominion and destroyed the outpost.

Abathur next directed Kerrigan's focus to the world of Astrid III, where a feral zerg brood had been found. The brood had evolved zerglings that could mutate and hatch at an accelerated rate. Kerrigan reclaimed the hive cluster for the Swarm and Abathur assimilated the mutation, creating the swarmling strain. The swarmlings defended an attack from a nearby Dominion outpost and pushed to the outpost itself, destroying it.

Gameplay and Walkthrough
In the first part of the mission, the player must kill four karaks near their starting position. Upon doing so their zerglings will automatically evolve into raptors and additional raptors will be given to them. The raptors can leap up the cliffs to the northeast to attack the Dominion and destroy the outpost.

In the second part of the mission, the player receives control of a small base with a cache of minerals. They must rapidly mutate swarmlings to defend against a light Dominion attack wave, then attack the Dominion base. Swarm queens accompanying the base can aid in this with support fire and creep tumors. If the player's forces are lost, they can mutate more swarmlings as needed.