Psionic (Long War)

Psi powers have been significantly overhauled in Long War. Psi talent is now trained, not discovered, so with enough time and attempts, every soldier can be a psionic (barring some exceptions). There are many more powers distributed among more levels.

Training

Psi XP

After Xenopsionics are researched, soldiers will begin accruing Psi XP by going on missions. After the first round of training, they can also gain Psi XP by successfully using attack powers or resisting powers.^[Verify?] Reaching a threshold of Psi XP is required to undergo Psi training ('extra' PXP will not roll over for the next level, and will cap at the next requirement. Every round of training takes approximately 7-10 days, and is affected by the tester's will score.^[Verify?] After they reach the cap, putting them back in the Psi Lab for another round of training is required. You can see the current PXP level and cap in their Barracks profile.

The required training XP:

Level 1: 100
Level 2: 250
Level 3: 500
Level 4: 800
Level 5: 1250
Level 6: 2000, MC an Ethereal (each solider to achieve Psi Master must individually do this)

Plus Ability cooldown time, when abilities can or can't be used, soldier fatigue/rotation; the large PXP requirements encourage you to begin training and leveling Psionic soldiers at the earliest opportunity. Also note that the Volunteer must reach Level 5 before the Gollop Chamber can be used. Each listed PXP amount is cumulative, so not "plus another 250 PXP to level 2," but 150.

Success rate

The success rate of the training depends on the soldier's Will and the level. If the target Will for the level is equal to the soldier's Will, the chance is 50% (25% if More Than Human is active). It increases asymptotically to 100% at infinite Will and drops to 0% at 0 Will.

The target Will values are:

Level 1: 60
Level 2: 70
Level 3: 80
Level 4: 90
Level 5: 100
Level 6: 120

Limitations

MEC Troopers, Officers and soldiers with the Neural Damping gene mod are incompatible with Psi powers. They cannot undergo Psi training, and Psi-trained soldiers cannot become them.

Unlocking Psi powers

By default, only Psi Inspiration is available. Unlocking further powers is accomplished by performing autopsies and interrogations. One exception is Rift, which requires an in-battle accomplishment.

Psi-powers are now more effective based on the will score of the caster. For instance, Mind merge will add (will/25) hit points.

Note that several descriptions mention draining of will: repeated use may dramatically lower will for the rest of the mission, but will be restored once they're back in the barracks..

Effects on fatigue

A psi-trained soldier takes longer to recover from post-battle fatigue. The increase is 6 hours per level of psi training.^[Verify?]

Psi powers

One power from each level can be chosen. Note that some powers cannot be cast on the same target (ie: an Inspired soldier cannot be Merged with).

Level 1: Psi Inspiration, Mind Merge, Mind Fray
Level 2: Psi Panic, Neural Feedback
Level 3: Distortion Field, Regen Biofield
Level 4: Telekinetic Field, Psychokinetic Strike, Psi Shadow
Level 5: Mind Control
Level 6: Rift

Psi Inspiration

Psi Inspiration removes all harmful mental effects (panic, hallucination) from everyone inside the AOE as well as grants +30 Will for the next 4 turns. Unlike in vanilla, Psi Inspiration is not centered around the user but can instead can be targeted much like a rocket.

Mind Merge

Merge minds with the target, granting the target +25% critical chance and +1 health. ^[Verify?]

Mind Fray

If successful, deals 1 damage to the target and reduces its will, aim and mobility. Because of the greatly reduced damage (thankfully, since Sectoids now use it from day one) this is more of a debuff than a damage ability.

Psi Panic

Cause target to panic, if the target's Will is overcome. Robotic enemies are immune. 2 turn cooldown. Note that panic has been changed a little in Long War so units will either hunker down or run, and never go berserk and take a shot. This makes Psi Panic considerably better than vanilla since it's now a reliable single turn disable.

Neural Feedback

Works near-identically to the vanilla gene mod, but with greatly reduced damage. Is always on. Also provides protection to nearby allies.

Distortion Field

Works the same as the vanilla MEC ability. Is always on. Watch out for grenade-bait formations.

Regen Biofield

Like the Elite EXALT Medic's ability, this will be activated when the Psion or a nearby ally receives an injury.

Telekinetic Field

Same as vanilla: +40 defense in a wide radius, centered on the caster.

Psychokinetic Strike

A cover-destroying, free-aimed psionic attack. AoE trigger field about the size of a grenade's blast, any destructible item that is at least partially in the field is entirely destroyed (ie; getting a part of a log destroys the entire log, barely clipping a wall will destroy as much as if directly hit with a rocket). Does not cause HP damage.

Psi Shadow

Similar to Mimetic Skin, save for that if the enemy gets around the full cover, it is immediately dropped. Also, Low Profile will allow you to move undetected to half-cover, but it will also be immediately dropped on arrival.

Mind Control

Same a vanilla--- granted, more difficult due to lack of Iron Will in the OTS. Also: alien weapons are no longer dropped intact if killed while MCed.

Rift

A highly damaging area effect attack. The secret to creating Rifts can only be found by Mind Controlling an Ethereal in battle.

Tactical Advice

Mind Merge vs Psi Inspiration vs Mind Fray

The one you choose of these three will be the main PXP-gathering method for that soldier, so keep in mind what opportunities they will have. For example, Snipers played in vanilla's Squadsight/Archangel style won't have the regular opportunity to Mindfray, but can take, say, the Double Tap cooldown turn to Merge with a mid-range soldier, boosting their chance for Mindfray or rolling a crit when firing.

Psi Panic vs Neural Feedback

Psi Panic is more proactive and is an excellent way to disable key aliens when (read: not "if") you get overwhelmed, while Neural Feedback can protect the soldier and nearby squadmates from psionic attacks, is 'always on', and return some damage for all the trouble the Sectoid's expanded ability set's been giving you.

Distortion Field vs Regen Biofield

Both passive abilities, it's a bit of a tossup between a nudge to maybe avoid a hit, or recover a smidgeon after being hit.

Telekinetic Field vs Psychokinetic Strike vs Psi Shadow

Three very good abilities, soldier class will be the primary decider, followed by playstyle. TK Field lasts one round and needs to be used, but is vastly more powerful than Distortion field; good for mid-range soldiers. PK Strike might be good for Rocketeers (or for any soldier you use in replacement of one) for when you want to take out cover, but don't want to spend a rocket or grenade (or the target is out of range for explosives). And invisibility is still a Sniper or Scout's best friend.