Encounters with the Inferi's
In 1979, Sirius Black's brother, Regulus Black tried to steal Slytherin's locket. (One of Voldemort's Horcruxes) He was killed by the Inferi's and told his house-Elf Kreacher to bring the real locket to the Black Mansion, which Kreacher did.
In 1997, Harry Potter and his headmaster Albus Dumbledore went to the cave on the search for Voldemort's Horcruxes. Harry was pulled underwater by the Inferi's. But luckily he was saved by Dumbledore who used a spell that casted a lot of fire wich chased away the Inferi's.