Mustard

Gas User is a villain affiliated with the League of Villains and a member of the organization's Vanguard Action Squad. He and the rest of his team serve as the main antagonists of the School Trip Arc.

Appearance
His appearance resembles a skinny teenager. He wears a school uniform along with a gas mask that completely hides his face. Under the mask, he has a wavy, light hair.

Personality
Gas User seems to be jealous, obnoxious, and angry towards dim-witted students in Yuuei as he rants. Also, he is pragmatic and merciless as he brought a gun, shooting towards Tetsutetsu's head.

Field Training Arc
Gas User began to move after he listened to Stain's declaration.

School Trip Arc
Gas User observed the summer camp alongside with Himiko Toga, Muscular, and Dabi waiting the orders to strike. Next night, he started the attack spreading his gas in the forest, incapacitating the majority of the students, while he continued to move his gas in the forest. Then, he encountered Tetsutetsu Tetsutetsu trying to attack him from the front.

Battles

 * Tetsutetsu Tetsutetsu & Itsuka Kendou vs Gas user: Lose