@Meanlucario  
@Digital Seapony  
I shall incorporate these into my existing headcanons.  
Between fandom and headcanon, they both have Pinkie Pie being very powerful.  
While Fluttershy is more wholesome and down to earth.  
But if we merge them both into a single being, something like a split personality.  
Maybe Fluttershy is not conscious of how powerful she really is, and while under normal Fluttershy mode, she will go about her normal routine as a normal Pegasus who doesn’t even fly.  
But like that one episode where Fluttershy takes over Rarities shop, if it makes sense for Fluttershy to change outfits and personalities faster than anyone can blink, she will do it,and act like it’s no big deal.

@Ping_chan  

@Background Pony #A466  
@Ping_chan  
Huh.  

 
We might be on to something here.

@Background Pony #A466  
I think… So? All 9 seasons are a pastel colored mush in my brain right now. XD

@Ping_chan
 
Isn’t it show canon that Pinkie Pie wore a Fluttershy costume, during some trouble in the Crystal Empire?

@Digital Seapony  
We’ve seen her skills at changing an entire outfit while out of view for only a second, she can probably switch between Fluttershy and Pinkie Pie faster than someone can blink.

@Digital Seapony  

I know that’s a joke, but wow is it easy to imagine fluttershy, a pony best known for crippling social anxiety and shyness bordering on isolation, to imagine an alternate persona that’s literally everyone’s friend and the life of every party.

Pinkie Pie was Fluttershy’s other personality all along, but nopony knew how to break it to her. That explains why they’re both voiced by Andrea Libman.

Series finale twist, Pinkie Pie was just a hallucination of the Mane 6. (Including Spike.)