Ectoplasm is one of the pro heroes who arrive at U.S.J with Tenya Iida as reinforcements. They arrive to Class 1-A under siege by the League of Villains. Ectoplasm uses his Quirk to take down several of the villains and rescues Denki Kaminari, Momo Yaoyorozu, and Kyoka Jiro.
Ectoplasm is present for the faculty meeting where the teachers agree to change the practical portion of the Final Exams. He is placed against Tsuyu Asui and Fumikage Tokoyami to take advantage of Fumikage's weakness at close range. He and the other teachers explain the changes to the exam to the students of Class 1-A.
Ectoplasm faces Fumikage and Tsuyu in the second battle inside a large labyrinth type building. Fumikage and Tsuyu start at the center of the structure and Ectoplasm spawns several of his clones around them. He warns them that he and the other teachers will do their best to crush the students. The students manage to flee into the upper levels of the building, but Ectoplasm keeps his clones in hot pursuit.
Although Ectoplasm's clones manage to overwhelm Fumikage a few times, Tsuyu's support allows them to destroy twenty-eight of them. The students reach the vicinity of the escape gate where the real Ectoplasm is waiting. He compliments the tandem for defeating his clones but asks them if they can deal with his next attack. Ectoplasm uses Forced Internment Giant Bites, a move that creates a giant clone of himself and traps the students inside it.
Immobilized, Fumikage orders Dark Shadow to escape in a last-ditch effort. Ectoplasm intercepts it and attacks with a flurry of kicks. Dark Shadow is unable to get past Ectoplasm with hand to hand combat and shortly retreats. They clash one final time, and Dark Shadow manages to handcuff Ectoplasm in a sneak attack. Tsuyu swallowed the handcuffs beforehand and gave them to dark shadow during its retreat. Having passed the exam, Ectoplasm releases the students from the giant clone and commends them on their clever synergy.
Ectoplasm, Midnight, and Cementoss join Shota Aizawa in his homeroom class to announce that Class 1-A needs to develop super moves.  They move to Gym Gamma, where Ectoplasm creates twenty clones for each student to fight in order to further develop their quirks and eventually create special techniques. This training is meant to prepare the students for the upcoming Provisional Hero License Exam. Ectoplasm uses Tenya's Reciproburst as an example of a super move.
Ectoplasm easily defeats Mashirao Ojiro during a sparring match. He tells Mashirao he moves predictably and they need to work on his fighting fundamentals. Mina Ashido tries further the range of her acid attacks and Ectoplasm advises her to do so by forming her hands in the shape of a nozzle. Ectoplasm challenges Momo Yoayorozu to create two things at once with her Quirk, and she does so with ease. Katsuki Bakugo excells during the training and even manages to destroy one of Ectoplasm's clones before demanding he make another.
Ectoplasm catches Izuku Midoriya staring off into space and hits him. Izuku explains he's struggling to develop a technique because of the injuries to his arms. Ectoplasm agrees that Izuku's Quirk is too inconsistent and if he doesn't have a fixed fighting style than he needs to focus on developing it for the day. Ectoplasm also supervises Rikido as he eats sweets and tells Ochaco Uraraka to focus while levitating herself. 
For the U.A. School Festival, Ectoplasm and Hound Dog are put in charge of security. As Izuku and Gentle battle, Hound Dog and several clones of Ectoplasm have caught a whiff of Izuku and Gentle Criminal's battle. Hound Dog and the Ectoplasm clones have reached Gentle and La Brava, as Gentle declares his surrender.