Grindylows
Background
Grindylows are octopus like creatures that live in the Black Lake.
During the events of Harry Potter and the Goblet of Fire (2005)
During the second challenge in the Triwizard Tournament, each challenger must collect a loved one from the Black Lake. Harry Potter hears Merpeople singing and heads in their direction. Fleur Delacour is captured by the Grindylows and removed from that part of the competition. Harry eventually comes to an area where he sees Ron Weasley, Hermione Granger, Cho Chang and Gabrielle Delacour tied to the bottom of the lake. Cedric Diggory frees Cho, and Viktor Krum saves Hermione after Harry is stopped from saving her by the Merpeople. Harry notices Fleur hasn't freed Gabrielle yet and frees her while the Merpeople are distracted. As he is carrying Ron and Gabrielle to the surface, he is attacked by the Grindylows. He uses magic to escape from the Grindylows and wins second place.