Ectoplasm is a tall, slender man with short hair, and completely blank eyes, tilted inwards. Due to losing his legs in the line of duty, he uses replacement prosthetics, and when in anything but his hero attire, he wears a pair of large glasses.
In his hero costume, he wears a tan cloak that covers most of his body, the area over his torso, and the high collar resembling that of a double-breasted trench coat. Underneath this, he wears a skin-tight black bodysuit with a golden striped neck area and a matching black helmet that covers his entire head, a jaw-guard attached over his nose and around his jaw, and circular mufflers. He also wears baggy dark gray pants and a pair of thin, lightweight prosthetic legs.
Ectoplasm is a steadfast and unrelenting hero, which has made him highly popular.
As a teacher, he desires the best from his students and isn't afraid to push them; he openly warned Fumikage Tokoyami and Tsuyu Asui he would do his best to crush them during their final exams. He also told them he was looking for his students to shine under pressure.
In the past, a villain took his legs. He now wears a proper prosthetic when in civilian clothes and sports a special lightweight battle prosthetic while in his costume.
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 and Fumikage to take advantage of the latter’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 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 Sato 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 Criminal battle, Hound Dog and several clones of Ectoplasm have caught a whiff of Izuku and Gentle’s battle. Hound Dog and the Ectoplasm clones have reached Gentle and La Brava, as Gentle declares his surrender.
Quirk and Abilities
Overall Abilities: Ectoplasm is a more than capable Pro-Hero and is among the strongest of the U.A. Faculty members. He excels at close range combat despite not having his legs anymore. Thanks to combat prosthetics, Ectoplasm's fighting style consists mostly of kicks in close range combat. This is why he was chosen to face Fumikage during the First Term Final Exam's practical portion. His close-range combat abilities exposed Fumikage's weaknesses and Ectoplasm easily overpowered Dark Shadow in combat. Ectoplasm is also very intelligent and has the ability to analyze Quirks in order to help students improve them.
Mathematics skill: As a high school math teacher, it is implied that he is at least somewhat skilled in the subject of math.
Clones (分身 Bunshin?): Ectoplasm's Quirk gives him the ability to produce streams of ectoplasm from his mouth and transform it into clones of himself. He can create as many as thirty clones at once, though, it is possible for him to push his limit to thirty-six on a good day. He can also produce a single giant clone of himself, although this sacrifices his ability to produce normal sized ones for the time being. His clones can be defeated with a strong blow, but otherwise, only Ectoplasm can dispel them.
- Forced Internment Giant Bites (強制収容ジャイアントバイツ Kyōsei Shūyō Jaianto Baitsu?): Ectoplasm shoots ectoplasm from his mouth and transforms it into a giant clone of himself. The giant Ectoplasm clone then overwhelms and traps the enemy with a huge bite. He first used this during final exams.
Prosthetic Legs: After a villain robbed Ectoplasm's legs, Ectoplasm wears prosthetic legs. In his hero costume, he switches to a lighter pair of prosthetic legs.