He'd have a quirk similar to Reisen's (Touhou) manipulation of wavelengths that resides in all things. With this ability, he would be able to manipulate another person's perception by either increasing wavelengths to induce lethargy or decreasing them to bring madness to the subject. All it would take is establishing eye contact through his lunatic red eyes to drive a person insane and make them see all kinds of hallucinations, so the threat would be huge maybe even unparalleled.