You have to be observant to be as successfully mischievous as the twins are. Imagine 11-year old Fred entering the Great Hall and when all the first years are marveling at the ceiling that looks like the sky, and the first thing he notices is a broom closet door behind the High Table, and he thinks that’s a strange place for a broom closet, and now he thinks Argus Filch is glaring at him for looking at the broom closet, and he turns to George to point it out but George is already pointing at the ceiling like everybody else - except wondering how to get above the sky, because there’s no way it’s actually raining on them right now.
Imagine Lee Jordan figuring out the credit card trick to open doors, except wizards don’t have credit cards, but butter knives work just as well (maybe better). Imagine George filling his backpack to the brim with butter knives because he wasn’t really sure how many they would need, so he just took all of them. Imagine Fred running into the Great Hall to tell George he figured out how to get on the roof of the Gryffindor tower, and he slips a bit, and he crashes into George, and 16 butter knives are clattering to the floor, and now Argus Filch is glaring at them again.
Imagine Lee and George and Fred climbing up to the top of the Gryffindor dormitories, and on the top floor there’s a rusty old ladder, and at the top of the ladder there’s a rotting wooden trapdoor with a 40-year-old padlock barely holding it shut. But alohomora doesn’t open it (maybe the caretaker before Filch put it there, and knew a charm or two), so the three boys convince a third-year to buy them a couple extra cans of butterbeer at the Three Broomsticks, and spend the next week and a half learning how to make padlock shims out of aluminum. And they spend the last night of their first year drinking the rest of the butterbeer on the roof of the Gryffindor Tower, toasting to the pranks they’re planning, and to the rest of the hidden places they’ll find, and to the lock picks that they ordered via owl post to practice with over the summer, and to next year - when they SWEAR this time they’d convince a seventh year to buy them proper firewhiskey for a farewell toast.
Imagine they’ve come back from the summer for their second year, having mastered picking seven-pin locks with the cores they ordered via owl post, because who knew that wizards didn’t think they needed more than four pins on any of their locks? (They all knew they needed to practice picking more pins than that, even if it would only be helpful in the muggle world - turns out it was, two years later when they busted Harry’s trunk out of the cupboard under the stairs).
Imagine they finally get through that broom cupboard behind the High Table in the Great Hall, and much to their delight they find a rickety spiral staircase that winds straight up to a catwalk that stretches the length of the Great Hall - and the catwalk sits above the enchantment that makes the ceiling look like the sky, and for the rest of the year none of the students can figure out why it looks like there are two suns (an enchanted jar with a flame inside, labelled “Tatooine,” sitting on one end of the catwalk), and the young professor who finally figures it out is a muggleborn who saw A New Hope in the cinemas the day before she was accepted to Hogwarts and hasn’t the heart to remove the jar.
Imagine Fred and George and Lee exploring the castle at 3am with the help of the Marauder’s Map, sometimes with Angelina and Alicia, and one time Cedric Diggory - but he didn’t know he was afraid of heights until it was too late, and he never went exploring with them again. Imagine all the nights they didn’t find secret passageways or roofs or underground tunnels, just a hole in the wall or an entrance to a pipe big enough for a person to climb through (or, a giant snake), and just when they are about to be disappointed they see a wall covered in carvings and ink scratches. Most of them look centuries old - (code?)names like “Daedalus,” or a picture of a ball of string. One of them looks more recent - an intricate drawing of a cat wearing glasses - and they find that in almost every place they go (but it takes another generation for Lily Luna Potter to wonder how old Minerva McGonagall really was when she became an animagus). And sometimes they find their good friends Moony, Wormtail, Padfoot, and Prongs - but usually it’s just drawings of a wolf, a rat, a dog, and a stag (never one without the other).
Imagine the night before they leave Hogwarts in their dust (and a wake of destruction for Umbridge to clean up), they sneak up to the Great Hall catwalk one last time, except this time they leave candles enchanted to float in a pattern, and as the sun sets over dinner the constellations are no longer the Big Dipper and Orion’s Belt, but words that read out “Weasley’s Wizard Wheezes” and the address for their new joke shop in Diagon Alley.
Imagine all the things they were able to do thanks to lock picks and butter knives, to aluminum cans and a couple hours of brainstorming. Imagine how they would have been totally fine without the Marauder’s Map, but all that much better for it. Imagine Remus returning to his favorite hiding spot as a teacher to find a handful of new carvings next to his little wolf on the wall. Imagine all the generations of Hogwarts muggleborns who teach the wizard-born children how locks work, and how doors work, and why they can always be opened, and why magic is great - but all it is is helpful, and what’s really great is what they can do when they combine magic and common sense and a little bit of whim.
Imagine one of the boys showing El a magic trick, like a card trick or a simple illusion, and El just eyeing them suspiciously for the rest of the day because all this time they had ‘superpowers’ and never told her until now.