Gas

Sleep Gas is an unnamed Quirk possessed by Mustard.

Description
Mustard's Quirk allows him to generate a sleep-inducing gas, which he can control at will. He is also able to sense the moves of anyone who enters the area the gas is spread on.

He is not, however, immune to his own gas, implied by the fact that he constantly wears a gas mask when using his Quirk. Being knocked unconscious will also cause the gas to dissipate.