@Background Pony #41D3  
Well, not all of them were reformed and know peace in Equestria. We only saw some of the Storm Creatures reformed and attended the Friendship Festival in the ending credits of the movie. 16-17 of them precisely. We can assume that some of the Storm Creatures were arrested to Tartarus or some parts unknown or executed by the E.U.P./Equestrian Royal Guards along with Celestia and Luna, some were burned to death by Spike as flamethrower used by Capper, some were sucked up by the cyclone that the Storm King had created, maybe some went to hiding or escaped or exiled by the Equestrians back to the Storm King’s realm that the Storm King, Tempest, and Grubber had abandoned, and maybe some are still present looking after the Storm King’s realm when he left to rule, conquered, and seized Equestria.

Theory: All the stormtroopers who were reformed eventually went underground (secretly) and that’s what Silverstream and her friends have come across.

@genervt  
No not that one. We all saw this one.

Let’s see here… shadows that bare the resemblance of the Storm King’s soldiers against a tiny, scared Silverstream.
 
Foreshadowing, perchance?  

@Background Pony #ACF3  
You mean this?  

Ooh I always did think the design for the storm guards were really cool. Really neat to see them on the show now.

@Background Pony #5F10  
My friend’s friend saw a leak of The Storm King in the EQG special. But he lost it cause it got removed. WHICH IS A HUGE SHAME! Cause I want to see that leak.

@Background Pony #3C16  
You do you. But I want for him to come back.

@Background Pony #ACF3  
I don’t, keep him dead!

@Background Pony #ACF3  
If it gives you any hope there’s still the chance he appears in that upcoming Equestria Girls. But I think we can rule this one out as a magic manifestation of Silverstream’s biggest fear, which would obviously be him.

@Darth Shy  
Still gonna pray they’re not… CAUSE I NEED STORM KING BACK!!!

@Background Pony #FA7C  
I’d be okay with that

@Background Pony #FA7C  
I’d be okay with that

@Background Pony #FA7C  
I hope they’re not.

they look like illusions

You gon get hugged.

I hope we figure out what the heck these things are.

Where can I find this video!?!

Where can I find this?

If anybody lays a finger on precious Silverstream they will face my unholy wrath.

@soundtea  
Or maybe it’s Twilight secret army that is waiting for the signal from her to take over Equestria.

@Background Pony #6C7C  
All this time twilight is building an army to take over Equestria.

@Background Pony #562D  
Take note of the crystal walls.  
One of the leaked synopsises is that the students find a hidden basement in the castle or school. These are likely illusions of a sort.

Execute order 66

Twilight s army