Ebony Dark'ness Dementia Raven Way frequently swears, usually intentionally, but sometimes a misspelled word results in an unintentional swear (for instance, Cornelius Fudge's name being changed to Cornelia Fuck and the words "sit" and "shirt" being misspelled as "shit").
Ebony's frequent swearing is implied to be because she's a goth as Albert Dumblydore is said to have sworn due to "trying to be gothic" and Proffesor Sinister is the only goth teacher and uses swears as terms of affection (as does Willow).
The first cuss word in the fanfiction was in Chapter One and it was used to describe Gerard Way as a "major fucking hottie".
Dumbledore is infamous for having sworn on his first line (namely "What the hell are you doing, you motherfuckers?!") and in Tara Gilesbie's author's notes since then, she's tried to justify his swearing by saying that he had a headache and was trying to be gothic. She also described his line "What have you done!" as "basically not swearing" and, even though that phrase was entirely non-profane, tried to justify it by saying that he was really upset.