This is the final mission. Tastidian tells you to go to the Psy Academy to ensure that it won't side with the Spriggats. Once you meet and talk to Piter, you regain all your memories and become exhausted. Once you fall asleep in your room, a man named Dean Lukas will be in front of you and ask you whether you want to side with the Psy Academy or with Tastidian.
Siding with The AcademyEdit
This is the canonical ending, where you must seek to kill the Shadowling Queen, Nelis. This is extremely difficult, so it would be wise to train as hard as you can. Once you feel you are ready (it's recomended to train your troops to have at least 40 HP, maybe more) go to Somnus, where you must face Tastidian. The first battle you have is with lots of Shadowling Soldiers and two Shadowling Guardian. The soldiers are pretty difficult to beat, but cornering them could help. You should try to take out the guardians as quickly as you can, because they are capable of doing massive damage. Once you've beaten them, you now have to fight Tastidian. He seems to have infinite health, but he doesn't. There are a bunch of shadowlings protecting him, which you should take out first. Once you've done that, keep as far away from Tastidian as you can while you heal. After that, try to consistently deal damage to Tastidian, because he heals every turn. His attack makes this pretty difficult to accomplish, since it damages all units surrounding him, but an effective tactic would be to have attacking characters have "turns", healing once they get too damaged to keep fighting and swapping with another. Another tactic is to leave the healer behind him alive until you have killed Tastidian, as while the healer is still alive, he will not move. As a result, you can attack him from a distance, while his attack will not reach you and he will not move toward you, rendering this boss laughably easy. The next battle isn't nearly as hard as the last one. It only has some Phantom Armors and Energy Golems. If you have Darkling, a good idea would be to shadowport behind enemies and attack them for backstab damage. Area-of-effect attacks are also helpful. The next battle wont be as easy...
Fighting the QueenEdit
Expect party members to die. A lot of them. Nelis is very fierce, and it doesn't help that there are energy golems and phantom armors protecting her. First off, destroy the energy golems, and then take out the phantom armors. While doing this, try not to get attacked by Nelis, as both of her attacks are insanely powerful.
After that, attack her with your most powerful units and don't stop. If one of your more useful units is in danger of getting killed, have someone else take one for the team by taking a hit with Holy Blast. (Your Hero can fill this role quite effectively with the White Orb equipped and a sufficiently-leveled Feedback / Vengeance attack to follow up with on the next turn.)
Basically, try to keep your healer, your main character, and main damage dealer alive until she finally goes down. And there, you've won the game!
Siding with TastidianEdit
If you side with Tastidian, you must fight Dean Lukas. This causes Anya and Guy to desert you. The fight that follows is extremely difficult. You must face the elite defenders of the Academy, and they get a free turn to pummel you at the very beginning. You simply must have someone (if not two someones) with Big Shield to make up for the beating you're going to take on your first turn. Make it your priority to kill the psy fighter with Light Bomb, or perhaps more easily, have Darkling distract him by Shadowporting out of formation and attacking him.
Fighting Dean LukasEdit
Dean Lukas has a high amount of health and a far-reaching, powerful Light Bomb attack. However, that is his only attack. Once you have defeated his defenders, simply pin down Dean Lukas with melee units and he won't be able to hurt you (as long as you keep your other units out of Light Bomb range).
After the MissionEdit
After this mission, you have won the game. You have the choice of either starting a new game, or a new game+. A new game plus keeps all your stats. Also, when you talk to Hellion about his chest, you get a hefty reward (5000 Gold).