Tekeli’li! Tekeli’li! Tekeli’li!

So i guess that’s the Chaos God of Parties then?

Headcanon: Pinkie Pie is actually an amnesic fragment of Discord, sealed in a pink gemstone after Discord’s defeat. Pink gems are known in the trade as pinkamena stones, and so when the Pie family cracked her out under the moonlight one night, they dubbed the filly they found Pinkamena Diane Pie. Because of her very nature, as soon as they saw her, she saw them. Immediately, the nascent liminal being impressed upon herself the DNA of Igneous Rock Pie and Cloudy Quartz Pie, making itself their daughter at its own genetic level.
 
Pinkie always knew she was no pony, but hid it… poorly. Thankfully, she unconsciously excreted an aura of “Somepony Else’s Problem”, whereby most ponies would ignore the abnormal, eldritch things that she did as “just Pinkie being Pinkie”. Twilight has come closer than most to cracking the secret, but Pinkie had to actively make use of her reality-warping powers to trick Twilight into giving up on figuring her out.
 
The Pinkie in Equestria Girls is the very same Pinkie, a higher-dimensional being, as viewed from another “angle”. She merely pretended to not know Twilight, and slyly helped her out by telling the exact story of who Twilight was to the Canterlot High equivalents of their friends.

Raise your hand if you always suspected Pinkie Pie was an eldritch abomination of some kind, pretending to be a pony and doing a poor job of it.

Twilight: Thats it, no more Lovecraft

(Presses intercom Switch)  
“Shelly, could you bring some wut into my office, please?”  
“Right away, Mr. Kraus.”

wut