When a new game is started, four difficulties can be chosen: Easy, Normal, Hard, and Impossible. Difficulty cannot be changed once the game has started.
In addition to affecting hard numbers such as damage rate or research speed, difficulty also affect diplomatic proposals. Easy difficulty will see more generous offers and gifts. In Hard and Impossible not only do the gifts disappears, you may actually be demanded to hand out territories.
Despite the name, with good tactic and strategy (and perhaps some help from this wiki), Impossible difficulty is not impossible to win for a veteran of the game.
Afterlight's Design Document (in Czech) may contains detailed difficulty formula.
|(ResearchTimeMod) Research speed multiplier.|
|(ManufacturingTimeMod) Production speed multiplier.|
|(TrainingSpeed) Training speed multiplier.|
|(TrainingDecay) Decay speed of partial Training.|
|Level Up Speed||1.4||1.0||0.85||0.75|
|(ExperienceMod) Experience multiplier. (Also apply to strategic)|
|(HealingNormal) Healing speed when not in ward or surgery.|
|(FactionSpreading) Speed of alien faction expansion.|
|(RaidDestroy) Chance that Rocket Base destroys intruders.|
|(HostilityBonus) Environment hostility level adjustment.|
|(AverageSquadsCount) Average number of enemy squad.|
|(EUdefaultLevelUpPoints) Enemy attribute budget baseline.|
|(HostilitySuitBase) Environment damage caused by suit breach.|
|(EnemySeeingMod) Enemy sensory range multiplier.|
|(EnemySeeingMod) Player character sensory range multiplier.|
|(DmgModFromEnemy) Enemy damage multiplier.|
|(DmgModToEnemy) Player character damage multiplier|
|(FriendlyFireWeight) Friendly fire weight adjustment.|
Comparison and Comment
Impossible research speed is slowest, to the point of nearly impossible to complete all items unless taking a very long game just for researching alone. Even for veteran player who intentionally pick and choose only essential researchs to do so, there would be half left undone when taking final missions without any intentional delays.
Another thing contribute to Impossible research slowness is speed of training and production rate in Impossible. Production rate mean there's simply no spare time to slot one or two Scientist/Technician onto labs, which lower the total number of scientists doing lab works. Impossible speed of training add a sense of VERY LONG time to train necessary skills.
Production rate in Impossible, by itself, is not that horribly pressing for a veteran who fully use looted weapons, use certain cheap weapons to maximum effect, and pick-choose very carefully which to produce. BUT to help the imbalance in research, loosen this rate would be one factor to consider.
Training speed in impossible is very limiting considering there's 3 training facilities without expansion. In the early stage, the feeling of crampness is one thing, but in late stage, due to high demand in labs and workshops, there's simply no spare time to train. Thus training time versus working time can be a very annoying calculation.
Thus, for players attempt Impossible game, it's advised to keep Research and training at normal, and production at Hard