Impossible Difficulty (EU2012)

Two shot hypothesis

The simple difference is this, an Assault Rifle's damage ignoring crits has a 66% chance of lethal against a Classic Sectoid if it lands. On Impossible, it's 33% chance of lethal, 66% chance of requiring two shots. There is a similar correlation, Squaddie weapons do 3-5 damage and against Classic 4hp Floaters and Thin Men, 66% for lethal. On Impossible, it's 100% of requiring two shots, ignoring crits. When you go further to Mutons, Beam Weapons again require at least two shots ignoring crits. Why does Impossible look more balanced and the difficulty curve is more steady? It is possibly the intended difficulty. In comparison, Classic looks strange as to why there is a sudden jump when it comes to Mutons to Impossible numbers, though they are provided more money to handle the spike.

The following is the chance of lethal considering 1-4 shots at a full hp Classic(3hp) vs Impossible(4hp) Sectoid, that are all either Flanked, at low/high Cover, or Overwatch shots.

Shot type	Flanked(+50 Crit)		Low Cover(20 Defence)		High Cover(40 Defence)		Overwatch(.7 penalty)
# of 65 Aim shots	C	I	C	I	C	I	C	I
1	56.33%	47.67%	31.5%	18%	17.5%	10%	30.33%	15.17%
2	81.68%	75.62%	54.9%	40.05%	32.5%	21.25%	53.77%	37.23%
3	92.53%	89.34%	71.11%	58.86%	45.16%	32.5%	70.30%	56.78%
4	97.01%	95.53%	81.87%	72.88%	55.70%	43.05%	81.36%	71.54%

Some observations:

• For the first mission, Overwatch shots and shots at Low Cover are practically the same. If you ever thought one or the other was somewhat good, here's the bad news.
• There is a much higher lethality chance in Classic but the way you should look at it is like this: there is about a 10-15% chance difference between Classic and Impossible for shooting at low cover and overwatching. This is the hard data that the same way you played on Classic will give the aliens a 10-15% higher chance of living and firing back. Shooting at cover or gambling on an overwatch trap are all bad plays.
• The amount of reserve shots for a particular play will dictate whether it's a good play or not. Impossible roughly requires one more shot than Classic to have even a similar lethality chance within the given chart.
• Instead of thinking of chance for lethal, consider the reverse: all but the four shots at a flanked Sectoid have less than a 90% chance of success, meaning there is a 10-85% chance, depending on the play, for the Sectoid to live and get another turn. Consider the concept that aliens outnumber you, not just for the first mission but every mission, and this chart, taking four shots at full cover yourself is already nearing a coin flip (not to mention these are actually the wrong numbers for them, they have 75 aim and Mind Merge crit chance boost potential. Three shots may be significant enough).

Patience

If anything, the most important lesson of XCOM and Impossible Ironman is a lesson in patience. Here are a few commonly made choices due to impatience.

• Taking a full distance blue move without retreat options nearby, which upon pod activation will leave that soldier defenceless. This will further pressure the player to go full offense to try to recover from that mistake, potentially leading to a death spiral.
• Not taking a full turn or multiple turns to reposition the squad. When changing the direction of travel, it may be necessary to spend a few turns just to reposition/reorient the Squadsight Sniper(s) and/or the rest of the squad to restore combat effectiveness before proceeding.
• After combat, stepping on an unsafe tile with remaining actions. If unsure of which periphery tiles are safe, it's better to not expose any soldiers until next turn.
• Firing first without considering defensive plays, such as breaking LoS and/or Hunkering down.

Tactical

• XCOM soldiers start with base 3 HPs (and +1 from Body Armor), a reduction that will have effects during all missions but making them very susceptible to KIAs from Sectoid Plasma Pistols at game start.
• The aliens will deploy on bigger numbers (usually 1 additional pod) during the 1st mission and specially on Terror Sites/UFOs. It can be a challenge to know how many pods are still inactivated.
• The AI will use grenades more, specially when facing Muton Elites or Heavy Floaters. After the aliens start fielding grenades the full cover positions in most maps will be very risky to use, since it will be blown away.

General Warnings

1. Missions at the beginning of each month are the most dangerous since usually new aliens will be introduced. April will bring Floater, Mutons (initially equipping with LPRs) in May, Cyberdiscs come in June and Beserkers in July. August brings Heavy Floaters, and Sectopods and Muton Elites will start appearing in September.
2. During Abductions/Terror Sites/UFO missions the aliens will have a number of packs tied to certain locations while others will be patrolling across the entire map. During the beginning of the mission and depending on the map you may expect to have those packs activated right in front of you.

Don't Panic

Panic management can be one of the biggest pains during the starting months on Impossible. The 2 Abduction missions that take place will leave the 4 unattended countries with a level 5 panic meaning that those 4 countries will leave the project at the end of the month. There are two main methods of dealing with this issue:

• Let It Ride - build only 1 satellite during March and launch it over the country that offers the biggest funding or to be able to secure a continent during April. This is the usual method if you are planning to do an April Base Rush strategy, where the main goal is to assault the Alien Base as quickly as possible for the panic reduction and the loot.
  • Advantages - You'll be able to use the credits to get the OTS/Foundry/Alien Containment up and running and advance through your research or get some squad upgrades or S.H.I.V.s quickly.
  • Disadvantages - Your funding will not increase much in April, forcing you to sell a lot of alien artifacts later on. You risk losing one or more useful continent bonuses.
• Satellite Of Love - build 3 sats before March 10th and get 5 engineers as quickly as possible before the 16th to build the 2nd Satellite Uplink. This allows you to cover 3 countries with sats and reduce their panic and, if you are lucky, a Council mission will take place in one of those level 5 countries, meaning 0 defections on March. This method is usually the first step into the Satellite Rush strategy, where the main goal is to get at least 8 satellites on orbit as quickly as possible.
  • Advantages - a lot of needed credits in April and keeping most or all options available regarding continent bonuses for later on.
  • Disavantages - you'll need §200 by the 10th to pay for the sats and an additional 6 engineers by the 16th. While it is easy to get the credits, it's also possible not to get an engineer reward on the 1st Abduction mission, sending this plan crashing back to Earth. And even with the first engineer award, the 2nd Abduction mission may not happen before the 16th, but to anticipate that possibility you can always try building a Workshop as quickly as possible. All of this means that there will be few credits left for any squad upgrades.

Make Your Own Luck

You lost a key Abduction mission or got 0 engineers, failed to capture an alien on time or got a Bomb Disposal Council mission and decided to skip to prevent getting trashed by Thin Men. Things went wrong, either by bad luck or mistake and you were too late to complete a necessary step of any of the previous strategies.

Start responding - cut your losses by cancelling satellites you won't be able to launch (you should always build them in batches of 1 for this purpose) and spend the money elsewhere. Think about what you need to do to get two satellite uplinks up in April, such as workshops, power and excavation. Or reinvest the cash in to squad upgrades and start thinking about what you need to take down the Alien Base at the end of April as a substitute for launching satellites. Or both, since it is even possible to build the second uplink and hit the base if you play your cards right.

Above all, don't panic - losing 3 countries in March isn't catastrophic; no continent bonus is indispensable and you can live without 7 countries as long as you stabilise things before losing the 8th. As they say, sometimes it is necessary to sacrifice a few to save the rest. And remember this definition of luck: "to be prepared when the opportunity presents itself".

Know The Map

Some maps are specially dangerous on Abduction missions, due to their openness, small size and/or general lack of full cover:

• Boulevard Euro
• Cemetery Grand
• Commercial Street
• Demolition
• Fast Food
• Highway Bridge
• Museum Euro
• Pier A
• Rooftops Const
• Small Cemetery
• Street Hurricane
• Street Overpass
• Train Station

Other Abduction maps are more favorable, with much better cover, more movement options and/or easy roof access.

• Bar
• Commercial Alley
• Convenience Store
• Gas Station
• Industrial Office
• Liquor Store
• Office Paper
• Research Outpost
• Slaughterhouse A
• Trainyard
• Truckstop

Take Cover

1. Hunkering behind full cover is the key to survive, specially in the first month. If your soldiers in full cover can be seen by the aliens, hunker down. It will give them a total of +80 Defense and reduce a Sectoid's chance of hitting to 1% without range bonuses.
2. Learn which cover cannot be removed by alien gunfire or explosives. Destructible cover can give a very wrong sense of protection and get soldiers killed.
3. Pull back whenever outnumbered, specially right after two or three alien packs activate all of a sudden.

Squad Equiping

1. When equipping during the initial months, the choice is between grenades or Nano-Fiber Vests. The first means the ability to remove cover, and weaken/kill single or clustered aliens. The second the ability to survive a single Plasma Pistol or LPR shot.

Classes

• The Heavy is the best starting class because of the Rocket Launcher and the Bullet Swarm ability.

1. The Rocket Launcher is a life saver during the first months due to its ability to kill clustered aliens with 1 shot. By adding Shredder Rocket each Heavy can carry the equivalent of two grenades, with even better range and damage abilities.
2. Bullet Swarm is arguably the best second best perk at the beginning. It allows the Heavy to Fire and Hunker Down in the same turn, protecting it from alien counterfire.

• Snipers are also very useful if they have Squad Sight, allowing them to fire without being exposed to the aliens.
• Assaults need to be carefully used. Run & Gun allows to outflank and Overwatch aliens but long dashes can provoke the activation of more aliens.
• Supports are underpowered until Laser Rifles or LPRs are available.

1. The Assault Rifle has a limited damage and critical chance ability compared to the other classes weapons.
2. The Smoke Grenade can only be used once or twice (if they have Smoke & Mirrors and doesn't give the same protection (+20 Defense) as hunkering down (double, or +40 behind full cover).
3. Sprinter is useful for spotting aliens and running away from trouble.

Aliens

Sectoids

• 7 tile blue move.
• HP increased to 4, preventing them from being killed by single Frag Grenade, although a well placed frag can take out the cover of three Sectoids, injure them and then leave them open to the rest of your squad.

Floaters

• 7 tile blue move.
• HP increased from 4 to 6, making Assault Rifles even more unreliable at killing them, however, their Aim remains the same as in Classic. Rocket Launchers still give 1 shot kills against both aliens.

Thin Men

• 9 tile blue move.
• HP increased from 4 to 6, making Assault Rifles even more unreliable at killing them, however, their Aim remains the same as in Classic. Rocket Launchers still give 1 shot kills against both aliens.

Outsiders

• 11 tile blue move.
• If not surrounded from two orthogonal directions at distance on activation, the Outsider will position offensively, allowing itself to be easily flanked unlike other non-flying ranged aliens. Or, at the very least, be in close proximity for an explosive.
• Also continues positioning aggressively after activation, though continued combat with an Outsider isn't preferable considering their shots against high cover have a 50% hit chance.

Chryssalids and Zombies

• Chryssalids have a 13 tile blue move. Stay 14-16 tiles away (firing range) or more if you have the option.
• On their third turn, Zombies will erupt and be replaced by a white Chryssalid utilizing that turn. Without proof of when a Zombie spawned, don't risk it. If you can, stay at least 14 tiles away anyway.

Mutons

• Remain the same as in Classic.

Drones

• HP increased to 7 on Impossible, 2 more than in Classic, turning them into a bigger nuisance. It also prevents Drones from being killed in 1 shot by suppressing them with a Heavy Plasma with HEAT Ammo and Mayhem.

Berserker

• HP increased to 25 from 20 on Classic and they deal 2 extra points of Damage on Impossible (for a total of 11 base damage).

Sectoid Commanders

• Similar to Outsider, but it seems once they start spawning two, Outsider or Sectoid Commander, only one goes offensive, the other positions normally but within vision.
• HP increased from 10 to 14 on Impossible. They also have a 35 Will bonus (25 on Classic), allowing them even better odds on Mind Control attempts.

Muton Elites

• +10 Aim (for a total of 100 Aim on Impossible), giving the best accuracy on the game. In addition, their health increased from 14 to 18 on Impossible, while their Defense remains at 30. This combination of high stats, their Heavy Plasmas and their numbers (just facing 3 can be a nightmare) makes them the most dangerous aliens on all situations.
• Can't be killed with a single plasma shot that isn't ability enhanced (i.e. Headshot, Shredder, Bring 'Em On) since it will deal a maximum of 15 damage with a critical hit.

Heavy Floaters

• Added 2 HP for a total of 16. Their mobility and bigger usage of Alien Grenades (3 tossing grenades at one soldier with deal 15 points of damage) makes them also very dangerous.
• Can't be killed with a single plasma shot that isn't ability enhanced (i.e. Headshot, Shredder, Bring 'Em On) since it will deal a maximum of 15 damage with a critical hit.

Sectopods

• Remain the same as in Classic. However, you'll face more of them during missions instead of just 1. Sectopods also seem to use more their Cannon to blow terrain.

Ethereals and Uber Ethereals

• +5 HP and +10 Will (25 on Classic), allowing them better odds on Mind Control attempts.

Enemy Within DLC

• Muton Elites Health Points have been increased to 18 on Classic (from previous 14) and 20 on Impossible difficulties (up from 18).
• No longer possible to abuse the Overwatch exploit to get aliens to freeze.

See Also

• Alien Stats
• Survival Guide
• Tactics