A ne’er-do-well fellow who set up a series of regurgitating toilets to confound the Muggles. Arthur Weasley spent some time investigating and hushing up the incidents in question (OP7). Willy was caught in the explosion of one of the toilets and was captured. He was quite badly injured and spent some time heavily bandaged. Willy happened to be in the Hog’s Head and overheard the first meeting of the D.A. He reported this to Umbridge and Fudge let him go without prosecution as a reward (OP22, OP27).
"Widdershins" = English for counter-clockwise or in a contrary direction