Willy Widdershins

From Hpwiki

Willy Widdershins is an insane wizard who was caught for jinxing Muggle toilets so that they regurgitate rather than flush down. He is a very big bother to Arthur Weasley . He bargained his way out of this story, by telling the Ministry about the students' meeting in the Hog's Head. He was finally caught for selling biting doorknobs to Muggles, some of whom lost fingers.