This was a great scene, but a childish part of me wanted to see the following:
 
Crystal: “Sombra, you will conquer and enslave the Crystal Ponies. And then you will free your fellow shadow ponies, and they will free me – and then you all will serve me forever as I conquer the world!”
 
Sombra: “Uh, yeah, just one thing. All those Shadow Ponies are as powerful as me, right?”
 
Crystal: “They will be as soon as both they and I are free. Until then we will both be weaker than you.”
 
Sombra: “And right now you lack the power to destroy or rule anything, right?”
 
Crysta;: “Yes, but upon my rise to power over you this will change – wait, why are you pointing your horn at me like tha – “ BOOM

@Darth Sonic  
from the looks of it, it would work on any dark entity.

@Background Pony #C616  
i don’t think they are ponies to begin with, sombra was just given a pony form to infiltrate them, but his true forms is dark smoke.

So the Crystal Ponies created a WMD designed to kill a certain racial group?
 
Delightful! Amore certainly seems like such a grand legacy for Cadence to aspire to!

that is intersting. the crystal heart was designed to overpower the shadow ponies, the umbron, indefinitely. and they will continue to i bet.

I have heard of worst origin stories

Sombra’s mom seems cool.

@Background Pony #2B6C  
When in doubt, sacrifice everyone. Mirror Sombra wasn’t the hero ponies wanted, but the hero they needed

@Background Pony #2B6C
 
Mirror Sombra was just a regular unicorn.

oh god… are you serious?!!!

@Abarekiller
 
Nah, there is no Crystal Empire in the alternate universe, which only means one thing…Mirror Sombra did one better and erased all the crystal ponies and all the umbrum forever from the mirror dimension.

Now we need a reverse version with King Sombra talking to a blue crystal as the Crystal tells him that the evil crystal ponies are afraid of him