Raynor's Raiders escorted the Agrian colonists to Meinhoff, but discovered an area infested by zerg. During the day the infested terrans did not venture far from their lairs and could be destroyed easily. However, during the night the infested emerged in large numbers and aggressively attacked the Raiders' base.
The refugees from Agria arrived on Meinhoff just as a zerg infestation virus was sweeping through the dense camps. Doctor Ariel Hanson appealed to Raynor's Raiders to halt the plague and save the refugees. Jim Raynor agreed, grimly noting the only way to stop it was to "burn it out." The task was made easier by the infested terrans' relative inactivity during daytime; the virus made them vulnerable to the high UV output of the local star. Rory Swann reverse engineered the hellion in time for the operation.
The infested and their nests were purged and the virus contained for the time being. The Agrian refugees departed Meinhoff in search of a safer place to settle. They eventually discovered Haven. On Raynor's advice, Hanson started looking for a cure to the virus.
The Kel-Morian Combine drew criticism for the deaths of so many refugees. The Combine denied responsibility.
The mission is divided into day and night phases. During the day, no enemy attacks on the base occur; this is the easiest time to sally out and destroy infested structures. This changes when night falls when the base comes under attack by hordes of infested terrans. During the first night, only infested terrans attack. After the second, infested marines join them. Finally, aberrations appear from the third night onward. Attacking infested structures during the night causes infested units to spawn from them and counterattack, but if the player is able to handle this they can finish the mission faster. On harder difficulties and the longer the mission takes, the more infested come out until, eventually, even a couple of buildings can still provide a constant stream of enemies. The length of the day phase also shrinks on harder difficulties, being 6 minutes on normal and 3 minutes on brutal.
The base is in the center of the map and has three entrances. The top right and bottom right entrances are initially open but are covered by a sensor tower. The bottom left entrance is initially blocked by destructible rock, and will be opened by the infested after several nights, or if considerable progress in clearing structures has been made early on. Bunkers with marines work well to hold the entrances and Perdition turrets are particularly useful, if available. After a period of time the player will automatically receive hellions and a factory, and should build a reactor add-on to construct more quickly.
The two infestors burrow during the day. The infestors may be killed during the night when they surface, or during the day with a detector, either by building a missile turret in the infestor area or with a raven or science vessel if the required research has been unlocked. They are most easily killed when their surroundings have been cleared during the day; only a few marines are required to take them down.
Reapers are well suited to this mission: they do extra damage against light targets and buildings, and their ability to leap up and down cliffs combined with their speed lets them retreat quickly when night falls, then leap back into action immediately at daybreak. Reapers are unlocked early on in The Devil's Playground, so acquiring them for this mission is a feasible option. Siege tanks are also viable, particularly as there is a cliff near the two north choke points. One or two tanks deployed to either choke here can render the player all but invulnerable. There is also high ground near the southern choke point, but the player needs a medivac dropship or hercules dropship to ferry tanks there.
Keep more than one attack group out during daytime. Infantry may systemically destroy infested settlements closest to base while hellions scout and wear down farther targets.
Clearing out all the buildings to the north and north-west of your base will stop your north-west entrance from being attacked. You can then use those units in the attack force, or move them to defend the southern pass that gets attacked half way through the mission. Unloading all your Bunkers during the day will help your attack force. Store them in separate command groups so you can bring them back to base easily when it's almost night time.
Army of Darkness
Complete mission on hard difficulty
Destroy 15 infested structures at night
Play the mission later in the campaign after more units are unlocked.
A force of hellions, marines, medics, reapers and marauders with some repairing SCVs should be able to take out enough buildings at night and stay alive. Damage the buildings during the day and finish destroing them as soon as night comes. Keep such a force out when it goes from night to day to avoid having to fight your way out of your base. Don't push your night force through the main attack waves unless you are desperate. Selectively damaging the buildings during the day make them significantly easier to destroy during the night.
Another option is to wait until Supernova and defend your base with siege tanks while killing everything easy at night with cloaked banshees. The enemy has nearly no detectors and you can kill them by day. 5000 Kills are no problem with that on brutal in the same rush in five nights. With this it is just shooting practice.