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Apart from fighting with firearms, an additional layer of complexity is added to combat in the form of Psionics where aliens can harass and disrupt their foes with their minds. Aliens' psionic abilities are used to create Panic (reduce Morale) or attempt Mind Control and force X-COM soldiers to turn on each other.
With the capture and interrogation of aliens capable of psionics, X-COM will also be able to use Psionics against the aliens.
To learn how to use and counter Psionics or how to ways to screen soldiers for Psionics see: Psionic Strategies
In X-Com Terror From the Deep, Psionics are also known as Molecular Control (M.C.). Except for the in-game flavour text, M.C. is identical to Psionics in all respects. Therefore, for the purpose of this article, all references to Psionics will also relate to M.C. Other TFTD term substitutions include:
|Mind Probe||M.C. Reader|
With the exception of the Mind Probe, X-Com soldiers are initially not capable of using any Psionic abilities. To do so they must first gain some Psionic Skill by spending a month or longer training in a Psionic Laboratory. Once they have gained some Psionic Skill, they can start accessing their Psionic powers by using a Psi-Amp.
X-Com Enemy Unknown
X-Com Terror From the Deep:
The equations governing psionics are as follows:
Attack Strength (AS) = (Psi Strength * Psi Skill / 50) - (Distance / 2) + Random Number(0 to 55) Defense Strength (DS) = Psi Strength + (Psi Skill / 5 ) + Difficulty If AS > DS then psi attack is successful Where: Distance is the number of tiles between the attacker and defender. Random Number is a dice roll that produces a value between 0 and 55 Difficulty represents the difficulty of the attack mode. Mind Control = 30, Panic = 10
The final Attack Strength is compared against the final Defense Strength. If the Attack Strength exceeds Defense Strength, then the Psionic attempt is successful.
The Distance between the attacked and defender adds a penalty to the Attack Strength at a rate of 1 for every 2 tiles. This means that soldiers that were otherwise able to resist psi attacks may become more vulnerable as they get closer to the alien launching the attacks. Conversely, the efficacy of the Psionic attacks worsen as more distance is put between the attacker and defender.
The Random Number roll introduces the element of chance into the attack. The random roll gives the weak or moderate Psionic user a chance to break through the defences that are of a similar or slightly higher Strength than the attacker.
These formulas differ slightly from the ones that appear in the Official Strategy Guide, but have been discovered through testing and code digs into the game executables. They are believed to be correct.
For an in-depth exploration of the psionic equations, including minimally and maximally effective soldier psi values versus the various aliens in the game, see Psionic Equations.
Alien Psionics Targeting
If any of your squad members, even a HWP, is visible to any alien during the Alien Turn, every member of your squad is at risk of attack from any psionic aliens, regardless of whether the spotter is psionic.
It should be noted that once you pass Turn 20, or if there are only 1 or 2 aliens left on the map, all of your squad members and their locations are revealed to the AI. This means you can expect a steady stream of psionic attacks after that turn if there any of the remaining aliens are capable of Psionic attack.
Summary of Alien Psionic Attack Strength
Figures are for Beginner level - Superhuman level
Fractional portion (if any) is rounded off.
Sectoid Leader: 50 - 67 Sectoid Commander: 60 - 80 Ethereal Soldier: 40 - 53 Ethereal Leader: 54 - 71 Ethereal Commander: 65 - 87
Given the formulas above, this means your soldiers need a psionic Defense Strength of 131 to be completely immune to a psi panic attack from a Superhuman Ethereal Commander, and a Defense of 111 to be immune to Mind Control attacks. A Defense Strength of 131 can only be achieved with very high Psi Strength and Skill (100 PStr + 155 PSk; 90 PStr + 205 PSk; etc.). However, aliens are typically going to be 10 or more squares distant from your troops, and if you give your troops extensive Bravery training, panic attacks become far less effective. Therefore, a Defense Strength of 100 plus Bravery at 80+ is generally sufficient to shrug off nearly all psionic attacks; this can be achieved by soldiers with a Psi Strength of 80 + Skill of 100, or even soldiers with 95-100 Psi Strength and little to no psi training.
The best defense is a good offense, however; by the time you have such high-level Psi troops, you will probably be able to mind-control nearly any unit on the map long before they can even spot you (see Exponential Mind Control).
Summary of Alien Psionic Resistance
Figures are for (any rank)/Leader/Commander, Beginner level - Superhuman level
Fractional portion (if any) is rounded off.
Grouped according to species, in order of increasing psi defence:
Muton: 25 - 29 Celatid: 60 - 69 Silacoid: 80 - 92
Reaper: 35 - 40 Floater: 35/40/45 - 40/46/52
Snakeman: 40/45/50 - 46/52/58 Chryssalid: 50 - 58 Zombie: 80 (all Zombies have Beginner-level stats)
Sectoid: 40/60/62 - 46/70/72 Cyberdisc: 100 - 116
Ethereal: 58/69/75 - 67/79/89 Sectopod: 100 - 116
A soldier with 80 Psi Strength & Skill can Mind Control even a Superhuman Sectopod 20 squares distant about 30% of the time; a soldier with 90 Str and 100 Skill will succeed 100% of the time at that distance. Each unit of distance between the target and attacker will increase the difficulty by almost 1.8% (or, if nearer, decrease it).
Walk-through for a Psi Attack
A number of factors affect the results you might see, especially for panic attacks. Here's a walk-through to make everything clear.
For the Psi Attack itself, only these factors matter:
- The Psi Attack Strength of the attacker; both Psi Strength and Psi Skill matter here (see equation)
- The Psi Defense Strength of the target; mainly Psi Strength matters here, but high Psi Skill helps a little
- The distance to target
Nothing else matters - the target's current Morale or Bravery, etc., do not affect the chance of a successful psi attack. The Psionic Formula alone determines the chance. It is described briefly above, and in much greater depth here.
If the attack is successful, the soldier gets 3 Experience points added to the counter that determines how much Psi Skill might improve when the mission ends. If the attack fails, they only get 1 point added to the counter. This is the only result of failed attempts; the target is not affected in any way by a failed attempt (but the attacker just ate some TUs, of course).
Past the fact that different soldiers are likely to have different attack skills and distances to a target, it does not matter if one soldier performs a number of attacks, or many soldiers perform one attack. Each attack is simply one attack, and each attack gives experience even if the target is already panicked to 0 Morale.
If you performed a successful mind control attack, the target is immediately MCed - and you can stop reading the walk-through here. But if you want to understand more about successful panic attacks, continue reading.
- All soldiers and aliens start battle with a Morale of 100.
- Recruits have Bravery from 10 to 60. The maximum possible value is 100.
- Thus, a successful panic attack can cause a soldier to lose from 10 to 100 Morale: 10 if they were a superman at 100 Bravery, and 100 if they were a wimp with 10 Bravery.
- All non-terrorist aliens have a Bravery of 80 regardless of game difficulty level, which means they lose 30 Morale with each successful attack. Terrorists have values as follows:
- 90: Celatid, Reaper
- 100: Cryssalid, Silacoid
- 110: Cyberdisc, Sectopod (although you can "successfully" panic attack an alien robot, as shown by the experience counter, it can't actually affect them!)
- While 30 Morale may not seem like a lot (and 80 Bravery may seem high), remember that the chance of a successful attack is based mainly on the target's Psionic Strength; Bravery is not involved at all. And, as the psionic formula shows, it is MUCH easier to panic a target than to MC it... panic has a +35.7% higher chance, due to the difference in the formula's constants.
- The amount subtracted from Morale is not subject to chance or variability, for a given target. It is always exactly 110 - Bravery. The variability comes from whether the attack was successful (above), and whether the demoralized target misses its panic roll (below).
- Panic attacks do not give any success or failure message. Here are some ways to see their Morale:
- Use a Mind Probe. It is not psi dependent, so psi-locked soldiers (not trained in the Psi Lab yet) can check the success of soldiers with low Psi Skill (and thus a low chance of inducing panic) when you first get Psi capability. But remember, the Mind Probe does not give psi experience.
- You can MC the alien and look at his stats. But this would freeze him for the current turn, and, of course, if you are able to MC, many won't bother with panic.
- If really determined, you can look at UNITREF.DAT offset  for the alien. Mainly only hackers or testers would do this, though.
- Also, working through the Psionic Formula for a few cases can give you a feel for how likely success is - i.e., how likely it is that you caused the alien to lose 30 Morale points. Even in the best case, though, a target must be attacked at least twice to have any chance at all of panicking, and at least 4 times to have a possibility of being at 0 Morale.
- If a unit panics or berserks, it always regains 15 Morale when done.
- Also bear in mind that a number of other events can also cause units to lose, or even gain, morale.
- For the record, units go berserk about a third of the time that they panic/berserk.
- Anyone interested in more details on the chance of being successfully psi attacked by aliens should see Psionic_Equations#Aliens_Vs._X-COM.