Fluttershy: “I may have kept just one.”

@Allonso  
Before you know it, there’s thousands Pinkie Pies running around. Celestia save us all.

Does it look like she’s coming out of the door - the actual wooden door - to anyone else?

Oh god it’s the pool of mirror all over again.
 
Welp. Bring on the FUN.

@Background Pony #7963
 
Personally i think Celestia is just going senile from old age and forgetting about half of the ancient and deadly crap just lying around equestria.

@Background Pony Number 17  
>How else do you explain all of the Sealed Evils In A Can that keep popping up during the series?
 
Being an immortal god princess must get pretty boring. Maybe Celestia leaves things like that lying around for fun, like surprise pranks against her future self and/or citizens.

@Background Pony #7963  
Twilight already blocked up the entrance to the mirror pool. But that doesn’t mean it couldn’t get unblocked; we didn’t see them setting a guard on it after all.
 
And I don’t picture Twilight setting up magical wards to warn her of unauthorized mirror-pool break-ins. Ponies seem to have a bad habit of solving whatever immediate crisis is confronting them, then forgetting about it. How else do you explain all of the Sealed Evils In A Can that keep popping up during the series?

Twilight! The Pinkies got out again!

 
Someone place a blocker!

Rev up those fryers

@Background Pony Number 17  
Or they could just block up the mirror pool. Twilight would have no difficulty in incapacitating large numbers of clones, and once they controlled the pool the threat of exponentially reproducing Pinkies would be eliminated. If she was feeling particularly lazy and/or sadistic she could just leave some kind of proximity detection spell running in the cave, hooked up to trigger a wide-area fireball spell (assuming such things exist in Equestria).

FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN  
FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN  
FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN  
FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN  
FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN  
FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN  
FUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUNFUN

You know, the writers could make the Pinkie Clone Herd a recurring menace. Just assume that one of the clones got away (like here: >>522043). Left with its dim sense of “Pinkie-ness” its sole motivation would be to have fun. And since more Pinkies = more fun, the clone would seek out the mirror pool and try to restore the herd Twilight had zapped back into it.
 
And just like The Thing, the ponies have to magically discombobulate the ENTIRE clone herd, because if even one is left, sooner or later the entire herd will be back.

We are doomed …. prepare the evacuation into the nearest 4th wall reinforced dimensions.
 
Celestia help us all ….

@Keith Mowz  
You’re clearly just not man enough to handle that much waifu material in one place.

YOU WERE GREAT  
-YOU WERE GREAT  
–YOU WERE GREAT  
—YOU WERE GREAT  
––YOU WERE GREAT  
—–YOU WERE GREAT..

Stam-PEDE!

@Keith Mowz  
The brochure said there’d only be a FEW Pinkie Pies!  
This is a TERRIBLE vacation!

There’s actually only 8, there’s an offscreen portal leading from offscreen to fluttershy’s cottage

id software’s newest game:
 
“Armed with a party cannon, you must battle through the hordes of demons Pinkie Pie clones and make your way through Hell Equestria to the source of the infestation: Fluttershy’s cottage. There, you must destroy close the hellgate mirror pool and free the equine race from the menace once and for all. You can’t fail, marine.”

Too many pinkie pies.
 
AKA, any.