The famous "Raptor Story" on GameFAQs's Current Events forum. At the beginning of the story, the first-person narrator crashes his sister's lesbian spin the bottle party and is about to make out with her...until she is revealed to be a velociraptor, something that was somehow completely unknown to the narrator. The twist is actually in the first act of the story, not at the end.
The parody creepypasta "DAY OF ALL THE BLOOD" wherein it is revealed that the man that all the blood was coming from WAS YOU!!! (OR HE WAS A LADY IF YOU ARE A LADY) AND YOU FORGOT THAT THIS HAPPENED
The comic, "Product"◊ follows a human grown in a test tube in a post-nuclear war world and the realization of what his purpose is. Who is he? The Kool-Aid Man.
A lot of creepypasta stories have tried to pull this off, of course, but arguably one of the most well-known and effective is the story Doors, in which the narrator witnesses a psychopath murdering his adoptive parents and kidnapping his sister. We don't find out until the last sentence that the narrator is a dog.
ThisFoundation Tale seems, behind the numerous redacted segments, to be about an ordinary college student who winds up lost in some sort of alternate hell-dimension. It's only by looking at the full title and paying attention to the last line that you can figure out the narrator is SCP-682, the Nigh-Invulnerable reptilian monster that the Foundation keeps in a tank of acid to stop it from killing everything because it finds our world "disgusting."
This satirical video from the YouTube channel "Circlejerk" (devoted to parodying Reddit) starts out like a typical rant about "social justice warriors" but ultimately reveals that one of the SJW Reddit moderators is actually John Cena.
"Killer On The Loose", an episode of streaming-only horror anthology series The Witching Season: It initially seems to be about a woman breaking into a house to get away from an escaped homicidal maniac, but in the end it turns out she is the maniac and the person she's been hiding from inside is her victim. A few standard horror tropes are played with to make the audience reach the initial conclusion: The man in the house looks villainous because he's sneaking around wearing a Jason-style hockey mask (as part of a Halloween costume), and you're meant to think he's already inside of the house because of Offscreen Teleportation, not because he was never outside chasing her to begin with.
"There is a Narrative Trick in this Story" is all about this trope, with the two characters discussing examples of how it can appear. Of course, as implied by the title, the story itself also uses the trope, with the characters turning out to be teachers, not students.
In Scootertrix the Abridged a major twist is that Rarity, up until this point being portrayed as a harmless Cloudcuckoolander, is actually a shapeshifting changeling who fled to Equestria from the Badlands because she was Never Accepted in Her Hometown. Since Equestria is currently at war with the changelings, this has major ramifications from this point on.