There may be some extremely creative and out - of - the - box X - Men fanfics out there that involve 'fart' in a one - of - a - kind way. For instance, a new mutant is discovered whose power is to turn invisible but has a side - effect of emitting a strange odor similar to a fart when using the power. This could lead to all sorts of comical and awkward situations within the X - Men story, like trying to keep it a secret from the other mutants or dealing with the reactions of the villains when they notice the smell.
While it's not a typical element in X - Men fanfics, one can imagine a scenario where a scientific experiment gone wrong gives a mutant the ability to create sonic blasts through a process that resembles farting. This mutant could then be an unexpected addition to the X - Men team, with the others having to deal with this rather strange power. The fanfic could explore how the team accepts this new member and how they work around this unique ability during battles and in daily life at the X - Mansion.