
The Psi Operative is considered the most powerful friendly unit in the game. Just like the previous incarnation of the class in the original game, the Psi Operative harness the mystical power brought by the alien invaders. Psi Operatives have similar powers with the Avatar and the Sectoids. In fact, the path to training a Psi Operative is by defeating a Sectoid and then performing a scientific autopsy on it (in the form of Research). After that, you have to complete the “Psionic” Research in order to build the Psi Lab Facility. The Psi Lab Facility have a very high cost, both in the materials department and also its power draw. The Psi Lab is the best candidate (after the Shadow Chamber) for the exposed coil because it bypasses the power requirement.
The Psi Operative is way different with the other classes not just in skillset, but also in its growth. The Psi Operative does not get promoted when it is able to complete missions or accumulate skills. Only by further training them in the Psi Lab Facility these operatives can learn new skills.
Skills appear randomly in three regardless of the strength of the skills. In the first training session, the most powerful skills might be available right off the bat. The preceding sessions will also offer three random skills, so always pick the most powerful of the bunch.
The Psi Lab Facility can also be upgraded to make room for another cell that allows two Psi Operatives to undergo training at the same time. If you want the skill list, go here.
Domination > Void Rift > Everything Else
This is how you prioritize. Always go for Domination and Void Rift if they appear in the choices.
Why?
Soulfire / Soul Steal
Soulfire + Soul Steal allows your Psi Operative to survive the entire missions without the need of Specialist specializing in healing allies. Forget about the healing, think about the damage that ignores everything.
Stasis / Stasis Shield
Stasis and Stasis Shield may look like they are useless skills. In fact, they are just that they are extremely situational. As much as possible a Psi Operative’s turn should be used in other much useful skills than using these. Stasis and Stasis Shield will indeed save your asses in some situations, but they are rather very specific. Learn these skills for completion’s sake or if you just feel using them. Remember, all of the ticking damage will also get paused, useful for your allies but for enemies, you basically are saving them.
Insanity / Schism
Insanity is a very useful skill and you should learn this first if both Domination and Void Rift are not in the choices. Insanity has a chance of mind controlling the target, so that is an added bonus, but this is permanent. Do not be afraid to let an Insanity-induced mind-controlled unit to let loose and die in the middle of a battle. As soon as they regain their control, you will have another unit to worry about.
I am not a fan of Schism, yes, there is an added damage but this will also mean that it could kill a unit during those times that should have triggered a Mind Control.
Sustain
Sustain allows your Psi Operative to survive when you are careless enough to send him / her to his / her death. Yes, he / she survived, but you won’t be able to use your Psi Operative for a few days because of being Gravely Wounded and Shaken or both.
Null Lance
Null Lance is a great skill in damaging enemies behind covers or those aliens which lined-up in a straight line. It does not have crazy amount of damage but it is a surefire skill with no chance to miss (except when units are in Stasis or other similar effects). Null Lance is the ultimate kill-skill because of its range and its nature.
Inspire
Inspire is a fail-safe option especially when things really get sticky. You probably find yourself triggering hostilities at the wrong time. Inspire can allow you to either allow your Specialist to hack one of the robotic units or a Psi Operative with an available Domination to get one of the units to act as a bullet / laser sponge for at least one turn as you desperately fix the situation you put into.
Solace
Solace will grant immunity to all the psychological attacks your enemies throws at your soldiers. However, a Shaken soldier (including the Psi Operative with the Solace aura himself / herself!) will still panic even if they are surrounded with the Solace aura. If one of your allies are under mental anguish, you just have send your Psi Operative to his / her location in order to extinguish them.
Fortress
A wonderful passive ability that allows your Psi Operative to survive environmental damages. This passive skill should allow the Psi Operative to maneuver across burning buildings to save civilian lives all over the place.
Fuse
Useful in ambush moments when all of these units are lumping in the same space. You can also detonate grenades from corpse.
Void Rift
Void Rift just wreaks havoc on enemies and the added bonus of Insanity is just cherry on top of what should be the most devastating psionic skill in the game.