We all know Harry got his lightning-shaped scar from the Killing Curse. However he was the first one to survive, thus the first one to obtain a scar from it. But Hagrid tells Harry that being touched by dark magic can leave scars.
Never wondered how you got that mark on yer forehead? That was no ordinary cut. That's what yeh get when a Powerful, evil curse touches yeh -- took care of yer mum an' dad an' yer house, even -- but it didn't work on you, an' that's why yer famous, Harry. No one ever lived after he decided ter kill 'em, no one except you, an' he'd killed some o' the best witches an' wizards of the age.
H.P.S.S Chapter 4, The Keeper of the Keys
So does that mean there are other dark curses that leave scars? We know that the Imperius Curse, the Killing Curse and the Cruciatus Curse do not normally leave any marks. Sectumsempra leaves a scar sometimes, if the person doesn't end up dying, like George and Malfoy for example.
When Snape had performed his counter-curse for the third time, he half lifted Malfoy into a standing position. 'You need the hospital wing. There may be a certain amount of scarring, but if you take dittany immediately we might avoid even that … come …'
H.P.H.B.P Chapter 24, Sectumsempra
But what other curses leave marks? Does anybody know what Hagrid was referring to? Surely no one else got a scar from the Killing Curse..