@PonyPon
Not sure if you intended the story to be a comedy, I love the idea of said changeling’s “alter egos” starting to bleed into each other when they’re scheduled for two “dates” at once. XD
So, you know how (almost) everyone universally despises the grimdark character-derailing Pinkie fanfic
Cupcakes, yet it’s referenced all the time in fan media? (Such as Pinkie innocently echoing one of her
Cupcake quotes about hacksaws or whatnot, having a bloodthirsty alter-ego, etc?) Well, not sure if this has been done, but imagine this:
A story introduces a character who’s a (much more kid-friendly) “expy” of
Cupcakes!Pinkie (maybe based on one of
the toyline exclusives [WARNING: TVTROPES LINK]). Pinkie, meanwhile, has deliberately secluded herself from her friends after fears that she may have innocently hurt them (perhaps in a similar incident to her treatment of Fluttershy in “Filli Vanilli”), and ends up befriending this not-Pinkie-but-based-on-
Cupcakes-Pinkie pony (let’s just call them “Hackney” as a placeholder name). Pinkie appreciates that her “being Pinkie” doesn’t scare or annoy Hackney and originally bonds quite well with this character, up until Pinkie gets hints of how twisted he/she is.
After some internal conflict within Pinkie, she confronts Hackney about his/her behavior, only for Hackney to respond with the usual “we’re not so different” villain song-and-dance. Which only strengthens Pinkie’s internal conflict until some moment makes her realize that, yeah, her guilt after accidentally hurting others does make her different from Hackney. And we get some sort of climatic confrontation where Pinkie tells Hackney to his/her face that they’re nothing alike (in a speech that can also double as Pinkie calling out why she would never act the way she does in
Cupcakes).
I guess it would all end up being pretty similar to the episode “Wonderbolts Academy,” with a hero meeting a shadow archetype of themselves without their morals.