This guide is on tactical combat for play XCOM: Enemy Unknown on Impossible difficulty. For advice on general strategy, see the Impossible Difficulty Strategy Guide article.
General information and advice[]
Sectoids — changes and tactical advice[]
On Impossible, Sectoids have 4 HP which matches XCOM soldiers who start with 3+1 HP. Given that a Sectoid's plasma pistol can deliver 4 to 6 critical damage, soldiers will often die from a single enemy shot.
- Soldiers should always be positioned behind full cover.
- Flank whenever possible. Scattering soldiers around the map can allow them to flank Sectoids more easily by breaking line of sight if possible and leaving one soldier as bait behind indestructible full cover while Hunkering Down.
- Use Frag Grenades to kill or weaken multiple enemies at a time or to destroy cover for a clear shot.
- If a Sectoid has Mind Merged with another, always prioritize the caster, possibly with grenades.
- Please note that the tactic demonstrated below will not work on XCOM: Enemy Within as Flanked or uncovered aliens will no longer freeze when caught in an Overwatch.
Thin Men — changes and tactical advice[]
On Impossible, Thin Men have 6 HP, and can cause critical damage of 7 to 9. When fighting them, it is advisable to never engage when the enemy has visibility on a squad member at the start of their turn. Cover is not very effective against Thin Men due to their Poison Spit ability, and they have a tendency to stay on Overwatch, making assault against them problematic. A player can counter this by retreating the squad far enough for the aliens to lose sight of them, then putting the soldiers on Overwatch. In this case, the aliens will often advance, and get shot down by reaction fire. If the enemy survives their turn, you can dash back for a retreat and repeat the sequence, or advance if the enemy is retreating. Just like Sectoids, they will also skip their turn, if they are flanked (or exposed) + overwatched. However, there is a low - medium possibility that they will shoot back or use Poison Spit ability, but still it's the best tactic to neutralize them. Best way to get into flanking position is to break line of sight and hide behind walls, trucks and bigger cars. They will advance towards the soldier's last position and use Overwatch most of the time. Take a peek at where they are, if Flanking still not possible, hide again and wait one more turn. Another way to get rid of them is explosives, two grenades or a Rocket Launcher shot can eliminate a whole group of Thin Men (a soldier's life is more important than a few Weapon Fragments) or just destroy their cover with one grenade, so they will be exposed to Overwatch.
Outsider — changes and tactical advice[]
On impossible difficulty, Outsiders have 90% aim instead of 80%, so they have 50% hit chance even if you are behind full cover. Best tactic is to clear the crash or landing site around the UFO and leave the Outsider alone. Don't get too close to the UFO or he could spawn if you accidentally see him for a second. After clearing the map, group up and approach the undamaged side of the UFO which has a "door". Move your soldiers near to the door but only open it on your next turn, when everyone has full movement. When the Outsider spawns, he almost always runs towards you to flank your soldiers. He only has 5 HP and you are close enough to get 100% hit with your soldiers, you can even use one grenade to destroy his cover and lower his HP to 2 if you want to capture him. Flanked (or exposed) + Overwatched tactic works on him as well. On larger ships, like Supply Barge if you find the Outsider first, he will call reinforcements to himself, so be prepared that all enemies will head towards you.
Pistols can be used to lower his HP instead of grenades, and an Assault ready to counter flank will generally dispatch him with ease.
Chryssalids — tactical advice[]
Chryssalids have 8 HP, so a combination of a Rocket from a Heavy soldier (6 damage points) and a Grenade (3 damage points) kills them right away. They don't have any weapons, so you are not losing anything by using explosives. With enough luck, it is possible to catch them in a single blast, as melee opponents tend to charge straight at your forces. Chryssalids have the Hardened trait, which reduces the likelihood of being critically hit, so Snipers will perform poorly against them. Since Chryssalids don't have ranged attacks and spend their turns on movement, Overwatch is very effective for granting free hits against them. If you can anticipate their approach by using a Sniper's Battle Scanner or reloading the game, you can essentially get a free turn against them by properly positioning with Overwatch. Additionally, highly ranked Assault soldiers with Close Combat Specialist ability get a free shot at an approaching Chryssalid. In conjunction with Run & Gun to get close to the enemy, and Rapid Fire for double shot, this can enable an Assault soldier to take three shots at the Chryssalid during one turn. On impossible difficulty a group of 3 Chryssalids most likely scatter, 1 or 2 will ran away from you to kill civilians and spawn zombies, which means more Chryssalids (they will kill civilians in fog war even before you encounter them, expect heavy zombie overrush), while 1 or 2 will attack your soldiers. Best tactic against them is explosives (as mentioned before) or you can outplay them, by keeping up the distance and focusing fire. Chryssalids have 20 movement, which means they can attack after 12 squares, if you can`t kill them for sure, fall back and let them run closer to you, so in the next turn you get almost 100% chance to hit and finish them off.
Exploiting save / load to save your soldiers[]
You can save your soldiers by reloading the game mid-mission, but if you repeat actions in the same order, all the same shots will hit and miss. The outcomes are pre-determined. This happens because the game "rolls the dice" for shots at the start of each XCOM turn. To get different outcomes, you need to change the order in which soldiers shoot and move, or move your soldiers on different positions. In short, you need to do things differently. By trying different order of actions, you can achieve 100% hit rate for your soldiers while never getting them shot. Unfortunately, this can't save soldiers from enemy melee attacks, because they always hit. However, this latest strategy is considered gamey.
Tactical Guide[]
Despite the fact that there are many types of missions your real goal is always the same — to eliminate all enemy forces. On Impossible the enemy has superior numbers, hitpoints and firepower so trading shots cover to cover will not work in most situations. In other words, more advanced battlefield tricks will be required to beat this hell of a difficulty.
Deployment[]
On the Impossible difficulty every detail counts so you should make sure your team is deployed properly. When you pick your soldiers their position on the screen 1-2-3-4-5-6 translates into the following deployment formation:
| Enemy | ||
|---|---|---|
| 3 | 4 | 1 |
| 2 | 5 | 6 |
| Skyranger | ||
Make sure to check the gear of all chosen soldiers, especially those returning from the infirmary. Until the "Launch Mission" button is pressed, a player can always go back to Engineering and make some more gear.
Scouting[]
In XCOM: Enemy Unknown scouting is very different from basic strategy games. The most important thing to realize is that enemies will NOT shoot at the soldiers in the same turn they are discovered. They will only reposition, mainly to cover, which is usually within the soldiers' visual range.
The best way of scouting is sending a single scout ahead expending only 1 action. For this action you can completely ignore any cover as you will not use it anyway. If some enemies are discovered they will take cover after which your Sniper(s) can fire from a safe distance using Squadsight and the scout can retreat back to the team, which is waiting in cover. If your scout is Assault Class, which is recommended, you can even use Run & Gun to activate Overwatch after retreating. If the enemies charge next turn, you can hit them with reaction fire and then finish them off in your turn. If nobody comes, repeat step 1.
If no enemy is found you can retreat back to the team and scout another direction next turn or you can move your team to the scout. When moving your team to the scout make sure you do not reveal any additional map squares. Failing to do is a good way to get your team wiped out. First move your Sniper if you need to. Then move your Heavy. They can both benefit from cover and should get the best spots in that order. Your Assault and Support soldiers should be then clustered as close to the first soldiers as possible so they can all take reaction shots if a patrol comes around. Once again, you are not going to get hit that turn so there is no risk of being hit by a grenade. Lastly, when moving your team, remember not to take any second action until the whole team is safely moved to the new location. This will allow you to run or fire if you accidentally discover some enemies on the way.
The "most common mistake" which can be seen in many videos is this: You send a scout to location A, find no enemies so you move a few more soldiers to that position and go Overwatch. Then you decide you want to support that team and send another scout to position B. Position B can be right next to position A, it can be well fortified and a logical place to move to. However, if you discover some enemies while moving to position B, you are in a tricky situation. Team B can fire but with only one action and without team A support. Team B can also retreat but that would expose team A. Therefore, never scout two locations in the same turns unless you have a very good reason or like to load a lot. Leaving one half of your team back may sound bad but in this game it works surprisingly well - same as clustering. Also, when moving soldiers, make sure all soldiers still have at least one action remaining. In other words, do not activate Overwatch or reload before moving your soldiers. This mistake is also nicely shown and explained in the beginning of this video.
Any class can scout but theAssault Class works best for obvious reasons. Run & Gun will allow you to Overwatch when you have to retreat to cover, Lightning Reflexes will enable you to look for enemies that are already active and the other abilities make the Assault Class by far the most durable. As scouting can require a lot of retreating, assault rifles are preferable to shotguns. Armor choice depends on the map. Basically, you should be able to check rooftops if there are any. Use the grappling hook carefully though, as it can sometimes take you to places that are difficult to retreat from. The Hover S.H.I.V. is a good alternative especially for missions taking place on multiple levels. However, few players spend resources to develop these on impossible difficulty.
Take your time. In all but two types of infrequent missions time is on your side. So, reload, improve your position and listen for those lovely noises that tell you where the enemy is. Most battles are not lost to a tactical mistake but rather to a lack of patience - you'll need a lot of it for Impossible Ironman.
Count your targets. If you engage more than 3 targets it is a good idea to take notes, especially early on. Knowing whether you have to use cover when scouting is essential and a loose enemy that drops a grenade on a clustered team is devastating.
Sniper combat[]
As said above, the enemy has superior numbers, hit points and firepower. What do we have? Snipers! Their long range is something the enemy lacks and you can abuse it in each and every mission. The key element here is Squadsight, which not only enables you to cover your team but can also be used for some "hit and runs" and "surprise shots".
Positioning the Snipers should be the highest priority. In bigger maps cover is not as important as line of sight. Plan a few turns ahead and place them so you don't have to move them all the time. They should be the first to get the Skeleton Suit, which can get them to position in turn 1. Archangel Armor is even better but doesn't have to be rushed.
The "hit and run" tactic is quite simple. Send a scout (Assault Class works best) forward spending 1 action, shoot targets with Snipers, pull the scout back. Repeat. This should be the standard scouting tactic and is further described in the Scouting section.
"Surprise shots" can be made using a Battle Scanner or Ghost Armor. To get the most of it, throw the scanner, wait a turn, put all but one snipers into Overwatch, then shoot the target with the most HP. Enemies will run for cover, suffer some reaction fire and then you have another turn to finish them off. This tactic is better than "hit and run" and should be used in small maps, places with bad cover and areas where you expect heavy resistance.
"Ghost Armor Annihilation" combines the most overpowered ability (Squadsight) with the most overpowered armor (Ghost Armor). All you need to do is to go invisible, approach the enemy and let the snipers have their fun. A team of four ghosts and two snipers can clear most maps without giving the aliens a single chance to fire. The same goes for the final boss who can be sniped all the way from the last room entrance. However, note that Close Combat Specialist trigger will break your cover whether you wish it or not.
Snipers should be the last ones to shoot in most situations. If you have a huge mob incoming, dispatching the first wave with other soldiers will save Double Tap for a harder wave that might be coming. Also, note that thanks to Opportunist, Snipers are better reaction shooters than all but Rapid Reaction Heavy Class. Due to Squadsight they can usually shoot anything that remains and they usually have a very decent chance to hit making them quite reliable at cleaning up. However, sniping first is an advantage when you deal with high HP enemies. The huge crit chance of Snipers combined with Headshot will allow you to one shot a lot of enemies so shooting at them with less potent squad members could be a waste. Keep in mind the huge crit chance of sniper rifles and expect that you will often deal more damage than is shown. Therefore do not waste your sniper shots on low hp targets that can be easily finished off by other team members.
You need 2-3 Snipers for this strategy to work on Impossible. Note that they synergize really well due to the Battle Scanner ability as each scanner can serve all your snipers. Suggested abilities:
- Headshot - Don't forget to use this one. Can be used with Double Tap. Yes, you can crit robots.
- Squadsight = Godmode. Snap Shot is really not an option here.
- Gunslinger vs. Damn Good Ground is often a matter of play style. Skeleton Suit will make it easier to gain DGG advantage in the early game. Late game Archangel Armor will grant easy access to DGG benefits, coupled nicely with better sight lines when flying on open maps. Whilst increased pistols damage may sometimes come in handy in close quarters, like buildings, ships and enemy bases, BUT, Squadsight snipers are usually positioned far away from enemies and out of pistols fire range, and Snap Shot snipers can move and shoot with their main gun making Gunslinger usefulness somewhat situational.
- Battle Scanner allows you to spot and kill whole groups of smaller enemies while Disabling Shot disables one enemy. Battle Scanner will make a lot of general engagements easier, but Disabling Shot can neuter single powerful units, such as Mechtoids and later Sectopods, allowing them to be dispatched safely. Disabling Shot is also worth noting as an excellent tool for assisting in capturing aliens - A reliable, small amount of damage as well as allowing easy moving in on the target without retaliation.
- Opportunist is a clear choice as Executioner is almost useless.
- Low Profile enables you to leave that full cover to your squadmates. Keep in mind that you have it. However, it rarely serves a purpose to Squadsight builds.
- Double Tap is very easy to use properly. In the Zone, used properly, will let you mow down multiple groups of enemies you had the ill luck of running into(especially good for Ironman if you're stuck with what found you). You may want DGG and Executioner for your In the Zone sniper, as missing is huge. ITZ may, however, mean that kill credit for large numbers of units go to the sniper, whilst Double Tap allows the already max-ranked sniper to soften up full-health units.
You should do your best to level your Snipers to Squadsight ASAP. Once there start worrying about the Snipers stealing all the kills.
Alternative Tactics[]
Instead of relying on Snipers, an Assault centric strategy can directly overpower the aliens on Impossible using the holy trifecta of Lightning Reflexes Assault, Sentinel module SHIV, and tanking close combat MEC.
Before researching the Sentinel SHIV the playstyle will be more conservative, with more reliance on Heavies and grenades.
Beeline techs / Key Breakpoints[]
- Asia is a good choice for managing Panic. As abduction missions increase panic in a whole region, Europe and Asia - with 4 nations each - will add the most panic per abduction. As you will always get your region bonus no matter how many countries of your origin region leave, starting in Europe or Asia reduces the chance of you losing access to a continent bonus. As Europe grants the most money for satellites, that makes Asia a good start.
- Satellites are always priority #1, so that makes Workshop, Satellites, and Satellite Uplinks key. The need for workshops depends on the number of engineers you get from missions. Generally, it is a better idea to take engineers as rewards for abductions because if you take the cash, you'll end up spending it on Workshops and Generators to power them.
- In Abduction Missions, find which abduction will prevent the most nations from going to 5 panic, then if there is a tie Sniper (if you need one) >engineers>money>scientists>Support/Assault/Heavy.
- Squad Size I and II are by far the most important Officer Training School upgrades and ought to be taken month 2, 3 at the latest.
- You want precision lasers by the first Terror Site mission - this will be the hardest fight in the game and it's night and day to have the Snipers with Laser Sniper Rifles and Laser Rifles / Scatter Laser out there to deal with the Chryssalid swarms instead of the default equipment. Some players, however prefer to go for Carapace Armor first, then straight to plasma weapons. This takes a lot of experience as you'll have to be able to capture a lot of aliens fast. Remember that even if a lot of civilians die you will still complete the mission and reduce the panic in the country. This is definitely preferable to losing your team so tread carefully.
- You want Carapace Armor by the time Mutons start showing up (month 3), so that soldiers can reliably survive a hit from their plasma rifles.
- Ammo Conservation is the most important Foundry upgrade, research Muton Autopsy and get 6 Muton Corpses stat for month 3.
- At this point, if you fed your Sniper kills, you should be able to snowball your advantages into a win. Success in the first 3 months is everything.