Alien Deployment (EU2012)

Alien Types

There are three main types of aliens present in the game: Commanders, Soldiers, Secondaries and Roaming. Commanders will only deploy on UFO missions, Soldiers can appear on Abductions, Council and UFO missions, and Secondaries will appear in UFO and Terror Site missions. All of these three types can also be present in Storyline missions. A final type called Roaming of aliens applies only to Drones and those are only deployed as escorts to larger robotic units or by themselves during the Alien Base mission.

'	Commanders	Soldiers	Secondaries
Missions	Storyline	Council	Council (DLCs)
	All UFOs	Abductions	Terror Site
		All UFOs	Large UFOs
		Storyline	Storyline
Aliens	Outsider	Sectoid	Floater
	Sectoid Commander	Floater	Chryssalid
	Ethereal	Thin Man	Cyberdisc
		Seeker (EW DLC)	Berserker
		Muton	Heavy Floater
		Cyberdisc	Sectopod
		Berserker
		Heavy Floater
		Mechtoid (EW DLC)
		Sectoid Commander (EW DLC)

Pod Composition

The aliens deploy their units in pods of the 3 types listed above. Each pod can have 1-3 aliens, usually all of the same species. Most alien species can be present on both the Soldiers and Secondary pools of pods, slightly favoring their chances of being randomly chosen for a mission. In the case of some specific aliens their pods can contain 1 unit of the pod species type, plus 1-2 escorts from another alien species:

• Berserkers (Mutons)
• Cyberdiscs (Drones)
• Mechtoids (Sectoids or Sectoid Commanders) (EW DLC)
• Sectopods (Drones)
• Ethereals (Muton Elites)

The type of aliens on each pod depend on 3 main factors: the month, the difficulty level and the type of mission.

Species Deployment

The Commander type aliens are usually introduced during specific Storyline missions: Outsider on first UFO mission, Sectoid Commander on Alien Base and Ethereal on Overseer UFO.

When choosing between the alien species, each month the game will create 2 distinct types of pods: Soldiers and Secondaries. Each month, the species in a pool will have a specific weight (calculated below as probability) of being chosen for either a Soldier or Secondary pod. On the next month the game will add new species to the pool and recalculate their probabilities of being randomly picked. The species present on the mission will be composed from these two types.

Some species have defined limits on the number of aliens that can be encountered during a mission. On the Impossible difficulty levels the limits are removed, making it possible for 5 Sectopods to appear during a Terror mission.

	March			April			May			June			July			August			September			October
Pod Type/ Alien Species	Sol	Sec	Limit	Sol	Sec	Limit	Sol	Sec	Limit	Sol	Sec	Limit	Sol	Sec	Limit	Sol	Sec	Limit	Sol	Sec	Limit	Sol	Sec	Limit
Sectoid	100%			28%			9%			8%			2%			2%			2%			3%
Floater				28%		3	36%	33%		15%	14%		2%	6%		2%	4%		2%	4%		2%	4%
Thinman				14%			18%			8%			2%			2%			2%			2%
Chryssalid		100%			100%			67%			57%			15%			12%			16%			16%
Muton							18%		2	31%			17%			5%			5%			6%
Cyberdisc										15%	28%	1	6%	18%		5%	9%		5%	11%		6%	11%
Berserker													23%	59%	1	20%	37%		10%	11%		13%	11%
Heavy Floater																20%	37%	2	10%	11%		13%	11%
Muton Elite																			20%		2	26%		3
Sectopod																				45%	1		45%	2
Seeker(EW DLC)				29%		1	19%		1	8%		1	2%		1	2%		1	2%		1	2%		1
Mechtoid (w/ Sectoid)(EW DLC)										15%		1	22%			20%			20%			13%
Mechtoid (w/ Commander)(EW DLC)													23%		1	20%		1	20%		2	13%		2

• Mutons will first appear on May with Light Plasma Rifles, will upgrade to Plasma Rifles on June (Classic and Impossible difficulties) or July (Easy and Normal).

Sources

• XComStrategyGame.upk game file, XGStrategyAI class, Enemy Within DLC version.
• Original data by wghost81, specifically from his Possible Aliens Tweaker mod to alter the species weight and limits, available at [Nexusmods].

Mission Deployments

The number of aliens present on each mission will also vary according to the month and difficulty level. but certain missions will have predefined alien counts, and some alien species may appear sooner than shown in the previous table. Some examples include the Slingshot campaign or the XCOM Base Defense mission on the Enemy Within DLC, which introduce several species ahead of their formal appearance months later. The Tutorials (Regular and Meld), along with the first Abductions, Terror Site and UFO missions have predetermined alien pod numbers and species.

Abductions and Terror Sites

Aliens on Abductions will consist only of Soldier types, while on Terror Sites the pods will be only of Secondary alien types. On the case of Abductions the difficulty level of the mission displayed on the Mission Control selection screen will also determine the number of aliens present during the tactical mission.

'	'	Easy		Normal		Classic		Impossible
	Mission Difficulty	Total Pods	Total Aliens	Total Pods	Total Aliens	Total Pods	Total Aliens	Total Pods	Total Aliens
Abductions	1st Mission	2	4	2	4	3	6	3	8
	Easy	2	4	2	4	2	4	N/A?	N/A?
	Normal	3	6	3	6	3	6	N/A?	N/A?
	Difficult	4	8	4	8	4	8	4	10
	Very Difficult	4	10	4	10	4	10	4	12
Terror Site	1st Mission	3	6	3	6	3	6	3	9
	Regular	3	8	4	10	5	12	5	15

Council missions

Council missions introduce another type of alien deployment besides pods, which is dynamic aliens, or the aliens who fall down from the sky during the mission. Council missions will only include Soldier species and Asset Recovery type missions will not contain any dynamic aliens.

	Easy				Normal				Classic				Impossible
Council	Total Pods	Pod Aliens	Dynamic Aliens	Total Aliens	Total Pods	Pod Aliens	Dynamic Aliens	Total Aliens	Total Pods	Pod Aliens	Dynamic Aliens	Total Aliens	Total Pods	Pod Aliens	Dynamic Aliens	Total Aliens
March	3	3	2	5	3	3	2	5	3	4	3	7	3	7	4	11
April	4	4	2	6	4	4	2	6	4	5	4	9	4	8	6	14
May	4	6	2	8	4	6	2	8	4	6	5	11	4	10	6	16
June	4	8	3	11	4	8	3	11	4	10	6	16	4	10	6	16
July	4	9	4	13	4	9	4	13	4	12	6	18	4	12	6	18
August	4	10	6	16	4	10	6	16

UFOs/Alien Base

On UFO missions the game introduce the Commander type aliens, deployed as a single Pod, usually located at the bridge of the UFO, although its location can vary, along with Soldier pods in all UFOs, and Secondary pods on the larger alien craft from Abductor upwards.

Difficulty	Easy		Normal		Classic		Impossible
UFO	Pods	# Aliens	Pods	# Aliens	Pods	# Aliens	Pods	# Aliens
Small Scout Crashed	3 Soldier	4 1-3	3 Soldier	4 1-3	3 Soldier	4 1-3	3 Soldier	4 1-3
Small Scout Landed	3 Soldier	9 1-3	3 Soldier	9 1-3	3 Soldier	9 1-3	3 Soldier	9 1-3
Large Scout Crashed	4 Soldier	7-9 1-3	4 Soldier	7-9 1-3	4 Soldier	7-9 1-3	4 Soldier	7-9 1-3
Large Scout Landed	4 Soldier	10 1-3	4 Soldier	10 1-3	4 Soldier	10 1-3	4 Soldier	12 1-3
Abductor Crashed	3 Soldier 1 Secondary	9 2-3	3 Soldier 1 Secondary	9 2-3	3 Soldier 1 Secondary	9 2-3	3 Soldier 1 Secondary	9 2-3
Abductor Landed	3 Soldier 1 Secondary	12 2-3	3 Soldier 1 Secondary	12 2-3	3 Soldier 1 Secondary	12 2-3	3 Soldier 1 Secondary	12 2-3
Supply Barge Crashed	4 Soldier 3 Secondary	9-15 2-3	4 Soldier 3 Secondary	9-15 2-3	4 Soldier 3 Secondary	9-15 2-3	4 Soldier 3 Secondary	10-18 2-3
Supply Barge Landed	4 Soldier 3 Secondary	16 2-3	4 Soldier 3 Secondary	16 2-3	4 Soldier 3 Secondary	16 2-3	4 Soldier 3 Secondary	21 2-3
Battleship	7 Soldier 4 Secondary	20 2-3	7 Soldier 4 Secondary	20 2-3	7 Soldier 4 Secondary	20 2-3	7 Soldier 4 Secondary	26 2-3
Alien Base	4 Soldier 4 Secondary	21 1	1 Soldier 2 Secondary	21 1	2 Soldier 2 Secondary	21 1	2 Soldier 2 Secondary	28 1
Overseer	1 Soldier 2 Secondary	7 3	1 Soldier 2 Secondary	7 3	2 Soldier 2 Secondary	10 3	2 Soldier 2 Secondary	12 3

• On the # Alien Total column values, Soldier + Secondary totals are in bold, on the Alien base they also include 4 Drone units. Commander Pod numbers appear in italics (not all confirmed).
• On the Alien Base mission the Command pod consists of a single Sectoid Commander.
• On the Overseer the 2 Secondary pods will be of Sectopod and Heavy Floater types on Easy/Normal difficulties, while on Classic/Impossible they'll be both made of Sectopods. The Soldier pods will always be Muton Elites, while the Commmander pod will consist of a single Ethereal and 2 Muton Elites.

UFO Pod Calculation

When the game is determining the final number of alien pods (excluding Commander pods) for each UFO it uses a special function (called ProcessPodTypes on XGStrategyAI class at the XComStrategyGame.upk file) that does the following:

• If the value of the total of aliens (the bold value on the # Aliens table column) is bigger than the number of possible pods (on the table as Alien Pods) multiplied by 3, then the total of aliens is reset to be the number of total pods * 3.
• Number of minimum possible pods is defined as the total of aliens / 3.
• If the remaining from the previous condition is different from 0 then it adds 1 to the minimum possible pods.
• Maximum possible pods is equal to total of aliens divided by 2.
• The final total of pods is equal to minimum possible pods + a random number, range going from the value of the maximum possible pods minus the value of the minimum pods and further added with +1.
• If the Alien Pods value is bigger than the final total of pods, remove 1 from the Alien Pods and repeat until they are equal.

As an example for the Battleship for Impossible difficulty:

• Number of possible pods * 3 = (11*3) = 33, # of Aliens = 26, so check.
• Number of minimum possible pods = 26/3 = 8
• 2 aliens remaining, so number of minimum possible pods increased to 9
• Maximum possible pods = 26/2 = 13
• Final total of pods = 9 + random (13 - 9 + 1 = 3). A Battleship can have between 9 to 12 pods, excluding the Command pod.

Regarding the Commander pod, the game also applies a specific function:

• For the Small and Large Scouts, it consists of a single Outsider, or it can consist 2-3 aliens of the Sectoid Commander/Ethereal types. (to confirm)
• For the Abductor, Supply Barge and Battleship, it can consist of 3 Outsiders (if landed). If crashed, it will have 2 on Easy/Normal difficulties or 3 on Classic/Impossible.

Sources

• XGStrategyAI class at the XComStrategyGame.upk game file, version 347752. The code version predates the release of the Enemy Within DLC so it the info may have been changed on EW. Talk page for discussion of specific code.