"This is for Despecho!" The hulking deformed shadow pony slammed it's hoof into a crystal guard, the purple gem pegasus shattered into pieces.
A ruby crystal pony who owned a flower shop ran, the umbrum leapt into the air, and landed hard on her, and jammed its horn into her back, and she shattered to pieces like a glass sculpture. "This is for Soledad!"
The next was a crystal foal who had been trying to hide under a cart.
"This is for Locura!"
Another crystal guard dove in, zig-zagging, keeping his distance, buying time for Cadence to arrive... Instead, the creature that looked like Sombra on steroids and being beaten with the ugly stick snarled. "And this! Is for me!" His red horn light up, followed by red glowing cracks covering his entire body, the crystal guard was causing in the exposition, and was reduced to crystal shards.
Cadence was finally able to break through the barrier.
"How... how did they... why did they..." Cadence didn't understand any of this.
"The Princess of the the Light of Pain wants answers?" Asked a filly's voice. It wasn't Cozy Glow.
"Ira?" Cadence's eyes widened.
Ira's corporal form was now much like Sombra's, shadow gray fur, red horn, green eyes. She was also the size and shape of a filly. Her face was stern and cold.
"I didn't want my brother to be alone, and I wanted to make sure my family knew he'd accomplished his dream. And the portal couldn't squeeze through two adult size corporal Umbrum. Squeezing through for him was worse pain than anything he said, my brother wasn't going to hold together much longer, so he wanted to make every moment count."
"Y-your brother?! That was Sombra!?"
"No! That was Odio! He's was in constant pain for a thousand years! We ruled this land of darkness before you crystal ponies even knew it existed! This unfeeling cold land welcomed us with open arms. Then YOUR wretched light came! And your reeking love magic!
"We weren't able to heal him from the damage the Crystal Heart had done to him at point blank range. That wretched crystal heart, and your light magic that makes us all fugly!
"The only thing that kept him going, was the hope that he'd be able to shatter a crystal pony for every Umbrum they destroyed. My brother didn't give up for a thousand years, he refused to give in or give up, and finally, he's accomplished his dream... as his sister, I'm so proud of him...
"If you want someone to punish, feel free to come after me, but that means opening the portal again, and allowing the Umbrum back into Equestria... and I have a feeling you won't be doing that anytime soon."
Ira began to walk backwards through the portal.
"WAIT! STOP!" Cadence tried to grab her with her telekinesis, but Ira turned to smoke as she slipped through, Cadence tried to cage her with a mass of crystal, but caging darkness is harder than it sounds, and the portal closed. "You can't just... you can't just... walk away..." Cadence said, looking around the square covered in shattered crystal ponies and one obliterated Umbrum.
(What happens with the VILLAINS do the 'and this is for!'?)