Survival Guide (EU2012)
This page is meant to contain all the info that don't fit on either the Strategy or Tactics guides or is common to both guides, along with links to specific strategies. If your tips, strategy or guide is very detailed consider creating a new page instead and placing the link in the relevant section below.
The RNG, Save Scumming, and You
Without delving deep into computer programming and algorithims: the Random Number Generator is the digital 'die' who's rolls decide the fate of the internal mechanics, odds, and outcomes of XCOM. Different actions and events are manipulated at different times by the RNG, and learning when and how means you can manipulate the game through what is known as "Save Scumming." In Scumming, what is done is that, through save-state management, you can remember what did occur in one attempt at a round of engagement in the battlefield, or certain events in the Base, and take advantage of RNG results.
As it sounds, Save Scumming is usually considered as a cheat. High risks and high losses are inherent to the spirit of XCOM as well, so you may be doing yourself a disservice (and spend a lot of excess time) in gameplay if you attempt to bring back every soldier in pristine condition. If cheating is not for you or if you have Enemy Within's Second Wave option of the same name toggled (although it affects shots on the battlefield only), you may still find this information to be informative.
At least on the PC version, you can also cheat with this method in Ironman during tactical missions, since the game will only save the current mission at certain points during your turn: closing the game and reloading from the save will bring the last save and you'll be able to take again any shots. Otherwise, you can manipulate save files through your PC's OS, to equal effect (if a bit more involved) as regular saving. A distinct advantage of this is that you can make folders to label savestates to difficulty/campaign, situations/progress, or whatever else you feel you need, as well as having backups for any long-term screwups, or if your savestates simply become corrupted. Note that your Steam account may make backups and transfers on it's own when you open and close it.
To take advantage of Save Scumming you need to understand what is affected by when the RNG produces it's numbers. Basically, there are two 'sets' of the RNG: the RNG as itself, and "Seeded" outcomes. In the normal RNG actions, the die is rolled when the event occurs. In seeded outcomes, a series of die rolls are made ahead of time. Sometimes, the actions are decided as well, while in others just the number that comes up, but you can take actions (or the order of actions) to take advantage via save scumming. Either way: note that, just like good old fashioned die, the RNG is only statistically random, but that dice have no memory.
First, your Base, and everything that happens in it: Base layout (what's solid rock vs natural caves, and 1 to 3 steam vent locations) is decided when a campaign is started. Perhaps more importantly, your monthly 'schedule' is rolled for at the start of each month, when you get your Council Report (obvious exception: in the case of March, the first month, it's rolled alongside base layout), and are thus seeded. The schedule will plot out when the various missions and detected UFOs occur (and on what countries).
- For Abductions, the countries are chosen, as said, at the start of the month (seeded), but the rewards each country gives (§, a soldier, scientists, or engineers) will be generated when the event 'popup' occurs (random). In the case of the "High Stakes" Second Wave option, the amounts are also random. With save scumming, while you cannot change what country is attacked (unless the savestate in question is before the end of the previous month), but you can change what reward (and how much/many) until a country you've prioritized to respond to gives the reward you want.
- Terror Missions: starting in April, these missions tend to favor continents that have high panic, are also seeded.
- UFOs are seeded, including the type, over what country, and landed or in flight. However, a UFO that escapes has a chance to summon a Battleship, which has it's own chance to shoot down a satellite. Of course, if a satellite is shot down, or a country withdraws due to a failed mission before the UFO is scheduled, this will change. For scumming purposes, what you can do is move and equip interceptors ahead of time (if you have enough time between a save state and a UFO appearance). The one exception is the Overseer UFO--- not the first appearance, which is seeded almost as normal (against when the Hyperwave Uplink's construction is completed), but subsequent appearances seem to 'react' to Interceptor placement (including if you move any around).
- Once in Interception and Air Combat itself, it is wholly random: a UFO's flight path may change on a whim, moving it closer or send it fleeing from an Interceptor. Once engaged, when either ship begins firing, if either's shot hits or not: it is entirely at the mercy of the RNG. So, saving before it appears, and (if you need to send more than one Raven or Firestorm after a UFO) between launches may help (if the first ship did particularly well), if you find your aerial offensive capabilities lacking.
- Enemy Within's EXALT Events: Due to their frequency, this may be confused for 'random'. In actuality, it focuses more on when was your last anti-EXALT action (such as Intelligence Scans, and/or sending out an Operative and following up on the accompanying mission), and will be seeded to that, but the effect will be random: Propaganda raises panic, Hacking drains all 'points' from research, or Sabotage taking your money. Note that Hacking will not occur if you have no ongoing active research, and no Sabotage if you're broke. Savescumming helps in that you can take note of which day an EXALT event takes place, reload, and time a Scan shortly before, extending the time between them, thus only needing perhaps 2-3 scans a month to keep EXALT off your back. If you want to take a "cheapskate" savescum route instead of spending money on Scans, either a) buy satellites/SHIVs/etc (anything that takes time to build), leaving a pittance of § for EXALT to Sabotage (and then cancel those items to get your money back afterwards), or b) start a new research project shortly before, and scum to let them Hack the few hours worth of research.
- Council Events: the odd one of the group, in that (on average) two events are scheduled per month. By 'events', this includes either Council Missions (Bomb Disposal, Extractions, etc), Requests for items/artifacts, or nothing at all. Of these three options, for the one that's taken for the first Council Event, it will be one of the other two for the second. The exceptions are the Slingshot and Progeny mission sets, which have their own scheduling rules.
Note that the mission types are shown in the Situation Room. Once you set out and go to the mission site and get to the battlefield: for each type of mission, there is a pool of maps available. These are randomly chosen from said pool after you hit the "Begin Assault" button on the previous screen. Additionally, many UFO assault maps (both crashed and landed) have another 'roll' for where the Skyranger will land (and your troops will begin). For example, you may start the assault on a Barge or Abductor near the front of the ship instead of the back. There are a number of exceptions, such as certain Council Missions, and Storyline missions, that you can know from the debriefing what map it will be (eg: escorting Sgt. Carlock will always be on the pier map, tutorial maps are always the same). Alien composition numbers will also be decided at this point (though, at least in the case of UFOs, what species will appear, and total numbers, is determined by the RNG back in the Situation Room, as evidenced by the Hyperwave Uplink-- though how many of each listed species may change).
Battle: this may be your focus on any save-state/RNG manipulations, and where you can turn nearly any situation into a victory; this is where where the number Seeds become most apparent. In essence, for at least a whole turn (both yours and the aliens), the RNG has already completed a number of dice rolls, and stores it in memory. In this case, the 'die' is 100-sided (while zero is an integer, a 100% shot is always guaranteed, and 0% always misses), and thus comes in the "Chance to hit" probabilities (with an additional roll for critical hits, when available). For whatever the unseen roll is, what your soldier needs to have is a higher aim score (aim stat and any modifiers, like S.C.O.P.E.s raise or being poisoned or suppressed drops). Psionics and stunning behave similarly, and seem to use the same 'list' of numbers. AoE attacks, as you aim them manually, obviously ignore the RNG completely (save for the 10% chance of Heavy rockets going off course).
For example, the RNG seed may give something like 85, 50, 2, 99 (which you cannot see). You have 4 soldiers, with aim of 60, 90, 80, 80. Assuming all other aim modifiers even out, if the soldiers fire in that order, soldier A and D will miss their shots, but B and C will hit their targets. Reloading, you make B fire first, and he'll land the shot, A can take either the second or third shot, and also hit, and soldiers C and D can take the third shot equally and hit, but the fourth shot will always miss, unless something gives the fourth soldier to fire either a 99% or 100% hit chance. Or, to put it more simply: when savescumming, use the soldiers with high aim if that order in the shots was missed before, and with luck, when the soldier with the lower aim takes a shot in a different part of the order, the Seed number will allow them to land a hit. This is the basis of taking advantage of the seeded numbers when taking shots. In the alien's turn this in effect the same-- and you can deny them landing any (at least any important/critical) hits with a number of actions, such as suppression, killing the offending alien, or using one of the various defensive techniques (hunker down, smoke grenade, etc).
When savescumming in the midst of battle, you may find that sometimes alien squads (particularly unactivated ones) will 'teleport' from any locations where you know they were. Be cautious of this. As for any active aliens, their movement uses the AI package, and thus isn't under the rule of the RNG--- but still having predictable behavior: if you take the same actions, so will they. So in a way, enemy movement is 'seeded', or at least manipulable.
Lastly, when returning to base:
- Artifacts/resources for most missions depend on your actions (how you neutralize enemies): shooting them, stunning them, or blowing them up.
- UFOs will have a roll for destroyed materials when shot down back in Air Combat. But, any damage you do during the mission (less alloys if UFO walls are destroyed, less Elerium if generators explode, and generators and computers themselves), will equal what XCOM will recover, so these are more dependent on your actions.
- Leveling soldiers: particularly if Hidden Potential is on (and can be supplemented by Not Created Equal, and the OTS's "New Guy" and "Iron Will" perks), your soldiers have a range of points each new rank can add to their stats. With Hidden Potential and Iron Will, your soldiers can get up to 13 points to their Will score each time they level. The increase to their Aim score is dependent on their class: 3 to 9 for Snipers, 2 to 6 for Supports, 1 to 5 for Assaults and EW's MEC Troopers, and 0 to 2 for Heavies. With Save Scumming, what you can do is save a state before the last action of a mission (usually shooting something in the face), and see the leveling scores in the Mission Results. To make it easier, you may want to make a logbook of sorts (eg: a .txt file, or handwritten notes), perhaps organized by class, so you can keep track of a soldier's Aim/Will scores as they level, reading from Base screens (since in-battle, the "Offense" score is their aim score plus any modifiers).
- While you could go all out and scum for Health and Movement bonuses as well: that is far too much hassle, in light of how, say, the odds of getting the max Aim/Will bonus for a Sniper is 1 in 64. For health bonuses: it's not quite as important, as long as any damage they do receive doesn't get through their armor. And Movement bonuses are the largest hassle to keep track of, as it is unlisted (save for the rare few Mods that modify the Barracks screen).
- Rookies who level will be assigned a class; re-rolling the class will require reloading from an in-mission save.
- If Training Roulette is on, leveling rookies will also have the random abilities rolled for at this point.
- Council reward soldiers' (and soldiers bought after New Guy is purchased from the OTS) random abilities will be rolled when the soldier is acquired.
- If Training Roulette is on, leveling rookies will also have the random abilities rolled for at this point.
Good times to save:
- Before the last action of a mission (specifically for stat-scumming)
- After a mission (particularly after getting high stat-boosts)
- After a good Random event.
- At the start of any turn with no active enemies, or at least you haven't been hit in Alien Action (past the armor HP, anyways).
Bad times to save:
- In the middle of a firefight, and soldiers have already finished their actions: you never know when you might get flanked by an alien you forgot about.
- After a soldier is KIA or Critically Wounded: you'll commit to that result if you do.
- Or otherwise right after the RNG finishes: like Vegas, you can't redo a roll or take back your bet after the fact of losing them.
It's also good to have multiple save states, such as having a save before a mission, another at it's start, and the quicksave slot for as the mission progresses. As mentioned, this is also excellent backup for in case a save becomes corrupted, or the game crashes or freezes and it's cause is 'inescapable' from your most recent save.
Strategies and Build Orders
From Normal to Classic
Making the transition from one difficulty level to the other can prove to be tough. The main differences to watch out for on Classic are:
- The +10 Aim bonus to the Aliens - suddenly Sectoids can be a lot more lethal.
- Soldiers have -1 HP less than on Normal - crucially this means Light Plasma Rifles can one-shot soldiers with basic armor.
- Thin Men/Outsiders now have 4/5 health - Assault Rifles are not much useful against them anymore.
- No OTS at the beginning - stuck to 4 soldier squads for a while until you get a Sergeant promoted and the OTS built. (With the Slingshot DLC, you can get Zhang fairly early in the first month to satisfy this condition)
- Panic now spreads throughout countries - all the world seems to be turning redder and redder.
- No extra satellite at the beginning - and less funding/base power/etc making resources scarce due to all of the requirements (OTS, satellite, research, engineering, etc.)
From Classic to Impossible
See page: Impossible Difficulty
See page: Training Roulette
An Army Of Four
See page: Classic Ironman An Army Of Four