OFF is a French RPG created by Mortis Ghost. It tells the story of the Batter, a mysterious bat-wielding individual who sets out to "purify" a strange land. While his mission initially seems noble, it's eventually revealed that purifying the world will destroy it, and that the Batter cares nothing for the lives of its citizens. The game is best remembered for its dark, surrealistic story and memorable cast of characters.
Fandomstuck OFF takes much of his appearance from two of the game's most famous characters: the Batter, and the fourth wall-breaking items merchant, Zacharie. He wears a white T-shirt with the game's red X logo on it and black undersleeves, similar to the Batter's jersey. He also wears Zacharie's mask and backpack, and has black tousled hair similar to him. Fandomstuck OFF wouldn't be caught dead without his trusty bat.
Fandomstuck OFF is best described as "mentally unsound." Outwardly, he seems perfectly normal, if a bit odd: he's terse and cool-headed, but can be friendly if one takes their time with him. Push him too far, though, and you'll see his real personality: a ruthless killer who won't hesitate to purify anyone who he views as "evil" or "impure." Fortunately, OFF considers himself a hero, and so saves the purifying blows of his bat for those he feels deserves it. For their parts, the other fandoms are careful not to push his buttons, and try their best to keep him on their side. OFF is usually one of the first fandoms to accept a theory, no matter how insane or convoluted it is, as long as it has some evidence backing it up. He can be somewhat egotistical about his status as one of the first big indie RPGs, but he has largely seceded that fame to Undertale.