Alien Deployment (Long War)
XCOM will end up conducting a variety of ground operations against alien forces, sometimes for the purposes of countering active alien operations like Terror Attacks and Abductions but equally as often for the purposes of raiding supplies and resources from downed or landed alien UFOs. In addition, the Council typically assigns XCOM with some critical mission each month from a random pool, from rescuing special VIPs to disabling bombs.
XCOM will encounter various alien types in these ground operations; each alien type is typically specialized for a unique role in combat. As Aliens further their research into humanity, their ground forces will gain increased health, damage, aim, and so on, and even access to many of the same kinds of perks XCOM utilizes, as befitting their designated role. Furthermore, as their research progresses the aliens will begin to field advanced alien types, and in greater frequency.
While a particular type may not be too threatening by itself, the various alien types tend to synergize well; for instance, Thin Men are good at pinning XCOM down into a long range war of attrition using their Acid Spit, good aim, & Suppression - this can allow the high mobility Floaters, a flying enemy type, to close in and flank XCOM. That said, aliens coordinate poorly at the tactical level, taking actions in isolation without considering any synergy with other units and without formulating any kind of cohesive tactical plan. Each alien evaluates the current state of the battlefield as its turn comes up, chooses an action based on it's AI routine (which varies from alien to alien depending on their capabilities and tendencies), and then executes it. It does not consider what other allies could do on their turn and attempt to synergize, nor does it consider the capabilities of XCOM & attempt to counter them. In short, aliens have a numerical and technological advantage but they're predictable and can be beaten with superior tactics.
Aliens typically deploy in Pods, or groups of 2-8 aliens which become activated in unison if any individual member spots an XCOM operative. Some select missions may involve "drop ins", or enemies that spawn mid-mission. Drop ins always spawn behind cover and overwatching, and are automatically activated. Drop ins are almost always Thin Men, though other alien types are possible depending on the mission.
Pods are typically comprised of one Squad Leader (often possessed with noticeably more stats and perks) & several regular troopers whose type is related to the leader and who have a chance to receive various upgrades dependent upon Alien Research. Later in the game, bosses with noticeably larger models and massive HP pools make an appearance in certain missions.
Pod composition is dependent upon the leader, with leaders tending to contain supporting troopers of the same or lesser type. For instance, Mechtoid pods tend to contain several Sectoids, whose Mind Merge ability can empower the Mechtoid with a powerful Psi Shield, while Cyberdisc pods tend to contain Drones which focus on repairing damage dealt to the Cyberdisc; conversely, pods led by Thin Men or Sectoids only contain units of the same type as the leader. The quantity of aliens in a pod is dependent upon overall Alien Research as well as the total number of aliens on mission; pods are rolled randomly and random numbers of aliens are added to said pods until all available units have been assigned. Quantity and quality of aliens are not dependent at all on Alien Resources, despite rumors to the contrary.
While members of a given pod do not coordinate amongst themselves any better than disparate aliens from different pods will, there is one significant mechanic which is pod-dependent: retreat mode. If a large portion of aliens of a given pod are destroyed (usually all but 1-3 depending on the original size), the surviving members of the pod will begin to fall back, retreating out of sight of XCOM and toward good cover or other, unactivated pods. The aliens will remain in retreat mode until they enter back into vision of XCOM again, though destroying more units from the pod is sufficient to resume the retreat. Aliens entering into retreat mode will be identified by visual and auditory cues; the camera will pan toward the alien shouting or talking, and one of your soldiers will mention that they're falling back.
Conversely, if XCOM is pushed back by the aliens, they'll call for reinforcements to hunt them down. In general, if active aliens exist on the map, aren't in retreat mode, and none of them has any XCOM operatives in sight range at the end of the aliens turn, they'll call all unactivated pods on the map (aside from the Command Pod, if any) to help them hunt down XCOM. Each unactivated pod will begin moving toward XCOMs current location inexorably, and short of retreating or being wiped out the only escape is to defeat all such enemies.
Pod Size & Distribution
Pods have a number of aliens that are directly dependent upon current Alien Research:
- Small (AR > 0): 2-4 aliens per pod
- Medium (AR > 120): 3-6 aliens per pod
- Large (AR > 240): 4-8 aliens per pod
While increases in pod sizes do not necessarily lead to more aliens on missions, extra aliens rolled that can't fit into any available pod are discarded. This has the largest effect during early Trap UFOs or Landed Large UFOs, which typically call for way more aliens than can fit in their Small Pods. To partially compensate, missions taking place while pod sizes are small typically get an extra pod or two to work with. Larger pod sizes typically means the same amount of aliens overall, just compacted into less pods - though later Trap UFOs and Landed Larges do have more aliens, as they stop discarding them due to having larger pods to work with.
Pods come in three basic types: Soldier Pods, Terror Pods & Command Pods. Soldier pods pull from a pool of most aliens and comprise the vast majority of pods encountered on all missions; Terror Pods pull from a slightly different pool. Command Pods only appear in UFOs and have relatively rigid compositions. Lastly, for Covert Operations, Exalt have special mechanics which govern the quantity and size of their pods.
- Soldier Pods: Soldier Pods are the most common type of pod, appearing as the majority pod type in every mission except Terror Sites & Covert Operations.
- Terror Pods: Terror pods are a special type of pod that only appear in Terror Sites, Large UFOs, Trap UFOs, Alien Base Assault, and Retaliation missions. They tend to have a greater probability of being higher-mobility aliens, and are the only pod which contains Chryssalids. EXALT also make an appearance in later months.
- Command Pods: UFOs additionally have a special pod called the Command Pod which contains a fixed number of aliens based on UFO type. Outsiders are the most common type, though Sectoid Commanders replace them on larger UFOs after XCOM assaults its first alien base, and Ethereals start appearing after the Ethereal Device is recovered. Thin Men may also appear in very early months in place of Outsiders on Large UFOs. Be warned: if a Command Pod spots XCOM and activates, it will immediately call all remaining alien forces on the map to its current location; this makes an early engagement against the Command Pod an incredibly risky affair.
- EXALT Pods: While EXALT have a chance of appearing in Terror Pods, they appear most often in Covert Operations. A typical Covert Extraction contains one jumbo pod of 3-15 EXALT (with pod sizes growing as the campaign progresses), as well as several smaller pods of 1-3 EXALT. If XCOM activates any pod and fails to kill them immediately, the remaining pods will begin slowly converging on XCOMs location. In contrast, Data Recovery contains several pods of 4-6 EXALT who behave as most pods do. All Covert Operations include drop ins or spawns of lone EXALT operatives who may or may not appear in cover and may or may not overwatch.
Aliens begin the invasion by taking over a target country to establish a base of operations, choosing a random continent that is not the same as the players starting continent and then choosing a random country in said continent. At some point in March of the first year, the chosen country will inexplicably leave XCOM, seemingly without warning; in reality, the aliens launched a large-scale operation called an Infiltration mission in which they capture and control the local leadership, setting up a Base to project their influence and coordinate operations. To prevent further Infiltration missions, XCOM will have to maintain a constant pressure over the aliens in the coming months, denying the aliens success in their ground and air operations so that they view XCOM as a more important Threat, or denying and starving the aliens of Resources; either is sufficient to prevent aliens from capturing countries instantly, though XCOM will still have to deal with the spread of panic which, if allowed to reach critical levels, provides aliens with a window to capture countries smoothly and easily without the use of the relatively expensive Infiltration mission.
The Aliens conduct various UFO missions in the air to achieve their nefarious ends and support their invasion effort. Missions are planned monthly, at the start of the month, and take into consideration Alien Resources and the Threat Level the aliens perceive XCOM to represent. Damaging, shooting down, destroying and/or raiding UFOs is one of few means of denying & depriving the aliens of resources; ironically, doing so also increases threat, so XCOM always finds itself caught between protecting countries from a surge in alien resources and protecting itself from a surge in perceived threat.
The Aliens primary strategy is to invade and take over the globe; they perform this by capturing countries, tending to focus on those adjacent to their existing holdings first before expanding outward to other continents. This tendency is governed primarily by an RNG that is biased towards focusing efforts on the highest Panic countries, though there is always a possibility of another target being chosen. Bombing runs and Terror missions are used to spread Panic to targeted countries to allow the aliens a window to infiltrate and control the local leadership and then install a base; with enough resources, however, the aliens will attempt Infiltration missions to capture countries directly regardless of panic levels.
The Aliens will attempt to Scout out and then Hunt down satellites to deny XCOM their primary means of engaging UFOs, with the RNG biased towards protecting their own bases from being raided before striking at XCOM-controlled airspace to deny XCOM air superiority. The Aliens' available intelligence on XCOM satellites is abstracted somewhat: they will spend their monthly Hunt missions - representing satellites they've located through other means - to strike at XCOM satellites directly; conversely, they'll spend their monthly Scout missions to try and locate satellites, spawning an additional Hunt mission over and above their monthly supply if the mission is successful. Where they are Scouting or Hunting is completely random, though they will always run the designated missions in countries with a Satellite over them.
If the Aliens consider XCOM a large enough threat, they will begin to focus their efforts on sabotaging XCOM operations directly. Above-average resources and threat is sufficient grounds to get them to send a ground team after your Interceptor Bases, though they'll only start doing so once XCOM has built it's first Firestorm. They'll even initiate an assault on XCOM Headquarters directly, though this requires a few months of maximum threat and resources to get the aliens to take such drastic & costly measures. High threat will also increase the likelihood that the Aliens will attempt to trap XCOM ground forces by sending a larger contingent of aliens to a given landed UFO than normal, though keep in mind that only UFOs that have successfully landed can be traps.
The Aliens also run various missions across the globe to support their invasion efforts: Research missions to give their air and ground forces a numerical edge in combat and Harvest missions to increase their supply of Resources so that they can field more missions and more powerful UFOs. Denying the Aliens the ability to do either helps in the long term, though the need to respond is not as dire as it is for other missions. On top of that, at high enough threat, the Aliens will often try to avoid XCOM-controlled countries when harvesting resources, though being forced to choose less optimal sites reduces the return. Lastly, Aliens will also conduct Abduction missions - for nebulous and mysterious reasons that may tie in with their overall purpose for invasions. Abduction missions don't particularly help the aliens or hurt XCOM, though failing to respond to them will still spread panic.
As the Aliens expand their coverage over the globe, they install Bases to exert pressure and control over the local government (likely via psionics). Where XCOM fails to present itself as an adequate threat and given a surge in resources, the Aliens will capture target countries directly with a large scale military operation; that said, a country too busy managing it's own panicking citizens due to unchecked alien activity will effectively hand itself over on a silver platter. Regardless of the method, the country will withdraw from the Council, and soon an Alien Base will be constructed on the target country to cement their foothold.
Alien Bases provide aliens with a selection of benefits:
- They exert control over a target country, preventing it from returning to the XCOM project while the base is intact. Captured countries will no longer provide XCOM funding & will not make requests to the Council; as a consequence, XCOMs means of acquiring additional income & personnel is disrupted. Finally, XCOM will be deprived of any country & continent bonuses associated with the given country, though XCOMs starting country bonus (if the aliens manage to capture XCOMs starting country) will not be removed.
- They provide the Aliens a monthly supply of Bonus Research, which steadily increases the capabilities of their air and ground forces. More research means more alien types and higher-leveled aliens, as well as more powerful UFOs.
- They provide the Aliens with a steady supply of Resources, which allows them to run more dangerous air operations more frequently & using more powerful UFOs.
XCOM can return the country to the Council by successfully assaulting the base, though locating them requires progressing far enough through the main plot and installing a Satellite over the target country.
Pod Type Probability
The following table determines the probability of a given pod having a given leader, based on the amount of Alien Research. Namely, for every 28 points of Alien Research (which, at minimum, is guaranteed to increase by 1 every day), a counter called iMonth increases by 1. Furthermore, for the purposes of Landed UFOs, iMonth is treated as being one higher than it currently is.
The leader determines the potential composition of the pod; for instance, a Mechtoid pod leader can be joined by other Mechtoids and Sectoids, while a Cyberdisc pod leader can be joined by other Cyberdiscs and Drones.
|Pod Type Probabilities|
|iMonth||Pod Leader||Soldier %||Terror %|
|Long War: Aliens|