Abathur located a concealed protoss facility on Cantar where several native lifeforms were being held for study. He identified a scantipede being held in the facility and that it had parasitic evolutions that could be of use, implanting parasites in entities it attacked that erupted upon death. Roaches invaded the facility and freed the killed the scantipede, assimilating its essence to mutate into corpsers. The corpsers destroyed the protoss warriors guarding the facility to escape into the wilderness.
On the planet Mehlus IV, the hostile environment provided roaches there with an adaptive mutation. Pools of liquid on the planet contained microbial organisms that generations of roaches consumed and bathed in. Most of them died but some of them adapted symbiotic relationships with the microbes and survived, becoming vile roaches. The vile roaches destroyed the protoss in the area to secure it for extraction.
Gameplay and WalkthroughEdit
In the first part of the mission, the player will command a force of roaches to kill a scantipede. The scantipede may kill a roach if forces are not microed, but this will not be a great loss. Once the scantipede is dead the player's forces mutate into corpsers. Send the roachlings they spawn into combat first to draw fire, and the corpsers can easily crush the protoss.
In the second part of the mission, the player receives control of a number of vile roaches. The forces in the way include several immortals, archons, and at the end of the mission, colossi. Microing the roaches to keep them alive is critical to maximize success, as is taking the time to let them heal between skirmishes. Abathur will replace any lost roaches and give new ones before the final battle with the colossi.
In early builds of the mission, vile roaches were replaced with prowlers, which were able to move while burrowing. This was added as a regular mutation option to roaches. In addition, corpser roaches were initially evolved from a drained protoss reservoir.