Vent: Why Brains Must Self Control Themselves: My Little Pony: Friendship is Magic: and its Everywhere: Final Friendship or IDK What I Wrote or What Tags it Needs but Here it is

And so the two are in The Summer Sun Celebration.

The party stuff are in their rightful location: The Summer Sun Celebration.

Announcement from The Summer Sun Celebration.

The mayor speech.

The reveal: no princess found.

Twilight preparing without a word.

"She's gone!" said Rarity.

"Huaaaauuhhh!"

"Oh. She's good!" said Pinkie Pie, surprised to see the nightmare cloud.

Gasps from ponies.

Twi is pissed on the inside.

Nightmare Moon reveals herself as Spike faints.

"Oh, my beloved subjects, It's been so long since I've seen your precious, little sun-loving faces."

"What did you do with our Princess!?" yelled Rainbow Dash angrily, as Applejack struggled to stop her.

"Why? Am I not royal enough for you? Don't you know who I am? Does my crown no longer count now that I've been imprisoned for a thousand years? Did you not recall the legend? Did you not see the signs? Do you know who I am?
Are you even listening?!"

Twi said nothing when Nightmare Moon asked questions, for Twi knows there is another.

An evil laughter rise to the ears of everyone in the Summer Sun Celebration.

Spontaneous fire appeared beside Nightmare Moon before it revealed Daybreaker and her speech to Nightmare Moon

"Oh Nightmare Moon. These are MY little subjects, and they belong to ME!" as Daybreaker attacks Nightmare Moon.

The nightmare battle has begun.

"There's two of these monstrosities?!" asked Rarity.

"And they're gonna tear eachother apart!" said a scared Fluttershy as the two nightmares crash through a wall.

Twilight chased the two nightmares, and every Ponyville pony followed. As the chase ended, three princesses and a light violet unicorn teleported to the middle of battle.

"You can't destroy me! I'm everything you want to be!" said Daybreaker, foolishly, to the Princess's doppleganger.

"No you're not! You are not real and you will never exist again!" Her wings brushed the magic beams aside as if they're nothing and repeled the beams back at the nightmares, leaving her to rest a short time.

Twilight enters the battle and said "You too." as she flung the six intruder's heads as if they're nothing so hard and fast they ceased to exist were they not real,

but they are merely unconscious instead, proving all of them are real:

Nightmare Moon,

Daybreaker,

the black background white cresent cutie mark Celestia,

the dark blue alicorn with the Princess's cutie mark,

the alicorn version of Twilight Sparkle,

and the dark purple cyan haired light violet unicorn.

The magic of these six intruders took them somewhere else.

Once again, Twilight beats herself over it.

"At this rate, Equestria will be no more forever." Twi speaks to herself as she runs somewhere.

In hearing her, Rainbow asks herself in the skies "Equestria no more? Forever?" as she sighs afterward and follows Twilight. It's already clear to Rainbow where Twilight is going:

to stop those six ponies.