Pinkie Pie: Mistress of repurposing.
 
Take the sneak suit you had for going into the Starswirl wing of the royal library. Add goggles for the Crystal Empire. Then sew on a few bits and a mask and it’s a Nightmare Night outfit, too!

@Cirrus Light  
And none of the ponies will realize what’s going on until the end of the episode when she finally reveals it, expecting them to have known all along.

love it

To recap:
 
“That’s a poster someone has in their room of a Nightmare Moon Construct in the form of Doomie disguised as Pinkie dressed as Doomie!”
 
And the poster is owned by Pinkie Pie who’s being a double-agent, making the Hive believe she’s Doomie being a spy in the form of Pinkie Pie.
 
Pinkie Pie -disguised as -> Doomie, on a spy mission for The Hive disguised as -> Pinkie Pie (making Pinkie a double-agent). This is a poster on her wall of -> a Nightmare Moon Construct in the form of Doomie -> disgused as Pinkie -> Dressed as Doomie.
 
Only Pinkie could pull off being a double-agent for the changelings, though XD

@Psychopomf  
And the poster is owned by Pinkie Pie who’s being a double-agent, making the Hive believe she’s Doomie being a spy in the form of Pinkie Pie.

@Archonix
 
I think skeletons are the biggest problem with insects being larger. They’d need an endoskeleton like larger mammals have, either in place of, or in addition to their exoskeletons.

The changelings we’ve seen are wolves in sheep’s clothing. This is a sheep in wolf’s clothing.

@HunterSClopson
 
People do dress up as terrorist though so it doesn’t really matter.  
 
 
 

 
At worst Pinkie is just being a little insensitive but really, who cares. She’s adorable as fuck.

@Archonix
 
at that point would they truly be an insect though?

@Frogster
 
Sure they can. The main limiting factor for insect size is the way they absorb oxygen. An insectoid creature with lungs and a closed circulatory system instead of spiracles and trachea could be significantly larger.

@HunterSClopson  
How often do terrorists feed on love?

I hate to be “That Guy” but isn’t this essentially the same as dressing up as a terrorist?
 
I mean, the country was just attacked by them.

@Background Pony #DA55  
Exoskeletons can’t take the weight of a creature that big.

@Background Pony #DA55  
Just makes it easier to hollow out and wear, like a suit of armor.

@ClownDicks
 
And Doomie just so happens to be wearing the Pinkie Costume from the IDW comics.

@Lium  
Changelings have skin? I always assumed it was some sort of exoskeleton or something…

“Time to scare more kids into giving me their candy!”

How does this only have 9 upvotes?

@Sjorge
 
That’s a poster someone has in their room of a Nightmare Moon Construct in the form of Doomie disguised as Pinkie dressed as Doomie!
 
There!

She actually killed a changeling and is wearing it’s skin.

So… That’s Doomie disguised as Pinkie dressed as Doomie? Is there a way to add another layer onto that?
 
Ah ha! That a Nightmare Moon construct in the form of Doomie disguised as Pinkie dressed as Doomie. Now someone add another layer onto that!

What if that’s not Pinkie dressed as a changeling, but instead is a changeling disguised as Pinkie dressed as a changeling. 0.0

Oh Irony!

How much are y’all willing to bet she runs into Doomie at a costume party?