Alien Missions (LWR)
During the long war against the alien threat, the skies are also part of the battlespace. Aliens will dispatch sorties of UFOs to further their goals during the war, and XCOM may respond in kind by sending out interceptors and the Skyranger to foil their missions in the air or on the ground. In other words, an alien mission always starts with an UFO sortie.
There are eight types of regular alien missions scheduled on the fly. The type of each mission is determined by the resources the aliens have, and how threatening XCOM is perceived to be. There are also two special mission types that occur irregularly. All ten mission types are listed and discussed below.
The aliens' choice of UFOs is limited by their level and resources, with the actual ship sent on a mission being chosen randomly - with equal probability for each - from the available pool. For example, if the aliens are weak then they will randomly send either a Scout or Raider for research; if they are strong however, then the large Abductor and Terror Ship will be added to the pool for the same mission.
Conversely, any damage and casualties sustained by the UFOs will cut into the aliens’ resources, likely limiting their options.
The aliens have a strategy in Long War, and tend to focus on geographic locations. Expect to fight them the most in the continent where they build their first base.
Missions themselves do not require Alien Resources to run if left unchallenged, but shooting down or damaging the UFOs conducting them does cost the aliens resources. Crucially, though, which UFOs are deployed depend indirectly on the alien resources as well as the Alien Level at the time the mission is scheduled. Specifically, Aliens add stronger UFOs to a pool if they have sufficient resources, choosing randomly from the pool when the mission is scheduled (with equal probability for each UFO type); Alien Level reduces the amount of resources the Aliens must have for the stronger UFOs to be added to the pool.
- If Alien Level 1-7, new types require 100% of their base required resources.
- If Alien Level 8-14, new types are possible at 72% of required resources.
- If Alien Level 15+, new types are possible at 40% of required resources.
A UFO will fly low and around the target country, attempting to confirm the existence of XCOM satellites there. Successful scouting missions will be followed up by a new sortie to hunt the compromised satellite. It is possible that the hunting UFO will be stronger or weaker than the scouting one, so the priority to intercept this mission can vary.
A scout mission can fail in four ways: 1) the UFO is shot down, 2) the UFO could botch the mission due to sustained damaged > 50%, 3) the target country could fend off the mission by itself, or, if all else fails, 4) the UFO could simply get unlucky. The odds of these failures happening are as follows:
- Downed: 100% chance of failure - if it's shot down they will always get nothing.
- Damaged: (100 - 2*(RemainingUFOHP%-50))% chance of failure - this means XCOM can commit less and gamble on merely damaging the UFO.
- Defended: (CountryDefense/2)% chance of failure - the shield representing a country's defense is shown in the Situation Room and is improved by fulfilling their requests; maximum chance is 50% with 100% CountryDefense.
- Damned: (60 - AlienResearch/15)% chance of failure - this means when the aliens have 900 research points, an unfettered scouting mission will always succeed.
The aliens will generally send 3-6 six sorties per month. As the game progresses the number of sorties sent decreases. As Alien Resources increase the number of sorties sent increases.
- Scout: Always in pool
- Raider: Aliens must have > 17% / 12% / 7% resources
- Destroyer: Aliens must have > 75% / 54% / 30% resources
- Battleship: Aliens must have > 100% / 72% / 40% resources
A UFO will fly at high altitude over a previously scouted satellite-covered country, seeking to destroy the satellite.
The aliens will prioritize getting rid of satellites over withdrawn ex-council-members, as they have bases in such countries and without a satellite over them XCOM cannot assault it. Next, the aliens prefer satellites that protect panicking nations, and in doing so potentially forcing said nations to withdraw XCOM support, and to be controlled by them.
Successful hunts will destroy the satellite in question. The base chance of success is 60%, or 90% on the second pass (30%/50% respectively if Stealth Satellites is researched. Damage sustained by the UFO will reduce this chance further, with 50% or less HP leading to an automatic failure.
Pertinent to this specific mission type, a 50% HP UFO will start flaring up in the aerial combat screen, as if it was being hit by multiple missiles continuously. When this happens, XCOM can order their interceptor to disengage, preventing further risks while stopping the hunt mission.
Note that the aliens can dispatch hunt missions directly, without needing to scout first; although this will only occur if alien aggression is high. The more aggression and resources the aliens have, the more direct hunt missions are sent.
- Fighter: Always in pool
- Raider: Aliens must have > 33% / 24% / 13% resources
- Destroyer: Aliens must have > 33% / 24% / 13% resources & Alien Level > 2.5
- Battleship: Aliens must have > 75% / 54% / 30% resources & Alien Level > 2.5
A UFO will fly NOE, land for a while, and then fly off. This mission will grant the aliens research if successful, increasing their level. This will slowly but permanently increase the capabilities of their ground troops and UFOs.
If the aliens have no resource (0% resources), the aliens will never undertake research missions; conversely, if they have many resources (100% resources), then the maximum amount of research missions will be performed. Otherwise, the aliens will adjust the amount of research mission attempts depending Alien Aggression and the amount their resources. If the aliens are not being very aggressive towards XCOM, they will be content with the tech they are currently fielding, thus will not carry out research missions; but as alien aggression increases, the aliens will try to keep up via research as much as they can afford it.
- Scout: Always in pool
- Raider: Aliens must have > 25% / 18% / 10% resources
- Abductor: Aliens must have > 42% / 30% / 17% resources
- Terror Ship: Aliens must have > 83% / 60% / 33% resources
- Assault Carrier: Aliens must have > 100% / 72% / 40% resources
A UFO will fly NOE and land in a randomly selected country. An unimpeded harvest grants the aliens resources, which will allow the aliens to field UFOs in greater quantity and quality.
If the targeted country has a satellite, there is a Alien Aggression / 2 chance that the aliens will re-roll its target once and will pay a price in the process. This represents the power projected by a strong XCOM forcing the aliens to settle for sub-optimal harvests. As the aliens' first choice for harvest is randomized, more satellite coverage means a higher chance that the aliens need to waste resource to even start a harvest mission.
The aliens' tendency to perform harvest missions is the exact reverse to their tendencies to send out research missions. If the aliens have minimal resources (0%), then a maximum amount of harvest mission is attempted (three per month); if they have too many resources (100%), then no harvest will occur. Otherwise, the aliens will harvest more when they are shorter on resource. Additionally, the aliens also prefer doing harvests when they are not being aggressive; in the presence of a strong XCOM they prefer more aggressive missions instead.
- Transport: always in pool
- Harvester: Aliens must have > 25% resources
- Raider: Aliens must have > 42% resources
- Scout: Aliens must have > 75% resources
Note that the UFO pool for harvest missions becomes less threatening the more resources the aliens have, and isn't affected by higher Alien Research as others do.
A UFO will fly NOE and around the target area bombing civilians. This mission will cause a lot of panic if successful. Uniquely, this is one of the few NOE mission types that doesn't land, and the only way to completely stop it is to damage the bombing UFO by at least 50%; although, damaging the UFO at all will still reduce the amount of panic created at the end of its mission. A successful bombing mission generates 9 panic in the country raided (reduced proportionally by amount of damage received down to 0 panic at 50% health) plus an additional 1 panic if the UFO has received no damage.
The aliens will send out more bombing missions if they have spare resources and a higher aggression level. With maximum resource and aggression level they will conduct multiple bombing missions per month.
- Fighter: Always in pool
- Destroyer: Aliens must have > 25% / 18% / 10% resources
- Battleship: Aliens must have > 58% / 42% / 23% resources
Multiple Abductors (2-3) will fly NOE to the multiple target areas and generate Abduction sites. A successful abduction will increase panic in the country and across the continent. Thwarting the abduction will decrease panic in the country and continent, but by a lesser degree.
Since abductions only provide a 12 hour response time, if a Commander is not careful, he could fail some of the abductions because of taking too long to fly to the other abduction sites.
Each successful abduction (a failed abduction for XCOM) grants alien research which leads to an increase in Alien Level. The council will offer rewards to XCOM for successfully completing an abduction which include: credits, scientists, engineers, and new soldiers. The difficulty of the abduction will increase the quantity or quality of the reward.
In many ways abduction is the least aggressive mission type; perhaps due to this, the aliens will scale back on abduction attempts if they are being aggressive. But the aliens still dispatch more abduction missions if they have more resources when they are not being aggressive with max resources. Conversely, if the aliens are short on resources, and are being highly aggressive (high aggression level), fewer abductions per month is attempted.
As the months progress, the number of abductions decreases by 20% per month, but there will always be at least 1.
This is a double sortie mission: At first, a Terror Ship will fly NOE and hover over the target nation scouting and planning for the actual mission. After a week or two an Assault Carrier will fly NOE to the target area and finally generate a Terror site. This means anyone with satellite coverage and interested in stopping the mission will have plenty of time to set up, though actually executing that is a different matter entirely.
The aliens will terrorize the most panicked nation adjacent to an alien base roughly 85% of the time, seeking to push them over the edge. Terror missions increase panic in the targeted country and continent per civilian killed.
Saving the vast majority of the civilians can actually lead to a decrease in panic. Losing or ignoring the mission will cause immediate country defection and an increase in panic continent-wide. Each civilian saved in a country that has not left the council will grant XCOM a 20 credit reward from the affected country (Modified by Campaign Length) (Increases by 10% per month).
There are only two ways to completely foil this kind of terrorism: by saving the vast majority of civilians during the engagement, or by shooting down the Assault Carrier before it could even deploy. Neither of these scenarios are predictable, and will probably be cost prohibitive to even try the latter. Only an exceptionally advanced and exceedingly experienced XCOM can pull either option off consistently. Otherwise the best a commander can do is to minimize the damage and make up for it elsewhere.
Nonetheless, terror missions are quite costly for the aliens as well. In fact, they cannot even afford it when they have the minimal level of resources. When Alien Aggression is higher, the aliens will try to launch more terror missions each month. One can prevent such an onslaught by depriving the aliens of resources which they desperately need for this kind of strategy.
Shooting down the forward scouting Terror Ship doesn't actually hinder the scheduled mission in any way. However, it's a lot easier to achieve, and it forces the aliens to pay dearly in resource cost for each such Terror attack they perform. In addition, it will grant XCOM a lot of looted resource and battlefield experience if the downed terror ship is successfully raided. It may not stop the looming terror attack, but it may very well help in the future.
As the months progress, the number of terror missions decreases by 20% per month and there will sometimes be none.
A Battleship and Transport will fly around the target area, followed by an Overseer inserting in to the target city. This mission will cause the target country to leave XCOM immediately if successful. Note that the final Overseer can only be detected if XCOM has the Hyperwave Decoder, so without one the country will appear to leave for no reason.
This is a very expensive option for the aliens, and as such they can only afford it with maximal resource available. And even then, the aliens won't yet try if they are being very aggressive, being too focused on hunting down XCOM satellites instead.
Aliens usually send an Assault Carrier to main base assaults. The aliens can only field XCOM Base Defenses if they have a lot of resources and high aggression; specifically, for every 3 months (not necessarily in a row) that the aliens are at maximum aggression level (100%) and a high resource level (>66%), an XCOM Base Defense will spawn.
If the aliens win a base defense it will damage resources and kill personnel - but it is not the end of the game, and can be recovered from.
For Air Base assaults, aliens will send an Overseer. The cost of failure of these missions is the destruction and/or severe damage of all stationed interceptors. Air Base Defenses are much cheaper, and have a chance to trigger every month that Aliens have an aggression level of >75% and resource level >50%. Air Defenses missions only begin spawning after XCOM constructs its first Firestorm interceptor.
This is a special mission. An Overseer will fly low around the target area. This mission is how the aliens communicate and co-ordinate their activities and is normally hidden to XCOM.
The aliens have many Overseers and shooting 1 down has no special strategic value.