Not much to build off here; one of these (the 2nd one) is just a response to someone asking for a story where a muggle-born deals with Umbridge via a gun.

The 1st one is just a silly little minific that I cooked up; it would have little relevance to any plot (unless you want to make a subplot about Flitwick seeking Snape for the Frog Choir), but it's cute nonetheless.

Neville's secret Boggart-banishing technique...

The DADA classroom, Harry's 3rd year. The lesson on defense against Boggarts...

"Finish it off, Neville!" Professor Lupin cried.

Neville strode forward, eyes glinting with mischief.

With a ~pop!~, the Boggart transformed back into Professor Snape, who raised his wand threateningly.

"Riddikulus" Neville intoned with confidence. There was a flash of light.

Nothing happened, save for the Boggart-Snape looking befuddled.

"Concentrate, Neville." Lupin urged.

Neville threw the professor a smirk, "Oh, I did, professor."

Then he stepped up and viciously kneed the Boggart-Snape in the balls.

Professor Flitwick stopped conducting the Frog Choir's practice for a moment and listened.

"Um, excuse me, just a moment," the choir stopped and looked at the professor curiously, "Does anyone know if anyone is practicing opera upstairs?"

There were murmurs and shrugs all around; the answer was clearly no.

Flitwick looked thoughtful, "Strange. For a moment there I thought I could hear the distinctive high-pitch of a countertenor."

"You see, I figured that if we can force the Boggart into a shape we find funny, we can also force it into a shape that has, well," Neville shrugged, "shall we say, a weak point."

Professor Lupin looked at the writhing, slowly disintegrating Boggart lying on the ground, and slowly nodded, "It was definitely effective, that's for certain...but please don't repeat it on the real Professor Snape."

A Mary Sue takes exception to Umbridge...

Professor Dumbledore looked bemused as Dolores Umbridge stood up to address the students gathered at the opening feast.

"Thank you for those kind words of welcome, Headmaster" she began to simper, "And I-"

BANG!

The words coming out of Umbridge's mouth were interrupted, as she ceased to have a mouth; indeed, the entirety of her head was missing, pieces of her skull and brain matter flying every which way and splattering the wall behind her.

There was a hush, the entire Hall completely silent, before Umbridge's still-standing headless body began spurting gallons of blood out of the stump of her neck.

"MARILYN OMEGA SUE!" Professor McGonagall suddenly roared, her eyes on the Gryffindor table where a ridiculously attractive girl was still holding a smoking gun, "I have told you before, .50 magnums aren't allowed at Hogwarts! Also, that was murder!"

The girl just smiled innocently, "Sorry professor, won't happen again." She paused as though thinking of something, before, "It wasn't murder, though. See, according to Obscure Wizengamot Ruling #3373-6594, when Dolores Umbridge attempted to assassinate me and Harry by sending dementors to my holiday resort, her violating legislation against cruel and unusual assassination made her automatically an outlaw who could be legally killed on sight."

McGonagall just grumbled, "Yes, well, 50 points to Gryffindor for slaying an outlaw, but, minus 2 points for possessing contraband items and making a mess."