Portable Swamp

The Portable Swamp was first seen when Fred and George Weasley planted it on the way to Professor Umbridge's Office. Once they fled Hogwarts to set up Weasleys' Wizard Wheezes in Diagon Alley, they left no instructions on how to remove the swamp, forcing Argus Filch to help students across it. Professor Flitwick later removed it after Umbridge was sacked as Headmistress at Hogwarts, leaving only a small patch. Although Flitwick claimed to have left it as it was "a good bit of magic", Ron Weasley believed it was actually left as a tribute to the twins.