The skies above Ponyville were dark, not because of a storm, but from the smoke of the burning buildings and the wings of the flying serpents that filled them. Nopony had known that the fire breathing beasts had been lurking in the Everfree, much less that they would be awakened by a simple fireworks display, regardless of how large it may have been. Of course, once they emerged from the trees, it was far too late to attempt to negotiate or apologize.

In the middle of the town hovered a purple Alicorn, her horn glowing bright enough to be almost blinding as she blasted out spells both to defend the ponies on the ground and attempt to drive away the enraged serpents. Sweat poured down her form, pooling in the bottom of the shield she had erected around herself. She pulled in the wind to disrupt the flying snakes, and emptied the river to douse as much of the fire as she could. Shields went up to protect the fleeing townsfolk from the incoming bursts of flame and the dive-bombing reptiles, and blasts of arcane energy shot out at the serpents that flew too close. She was holding her own, but she could feel herself weakening. It would only be a matter of time before her magic gave way, and the town would be defenseless. There was no magic that she knew that could stop this kind of attack, or, at least, no magic that she was permitted to use…

One year earlier…

"Twilight, I trust you understand the reason I'm teaching you these things." Celestia looked up at the ceiling of the room. They had gone deep under the castle to get to this magically sealed chamber, but she couldn't risk someone seeing them, even through scry sensors. Someone even picking up the usage of the dark magics that were being performed in these walls could lead to them learning some of them, though most required more raw talent than most unicorns possessed, or, could only be learned through… special means. She looked back down to her former student expectantly.

"Yes, Princess, I have to know these magics inside and out to truly know how to fight them. I have to be able to understand their strengths as well as their weaknesses, and be able to recognize them in even their subtlest forms. If I had known more about his magic, I may have stood a better chance of beating Tirek, not just stalemating him." She hung her head at her failure to lay the monster low that had hurt so many.

Celestia put her hoof on Twilight's shoulder, causing the smaller princess to look up into serious eyes, "This is not the time for self-doubt, Twilight. These powers have a will of their own, and showing weakness in their presence can be fatal. Remember, they all work to weaken your will to resist their use, some more than others. This is why you will not be using this next kind, but I will transfer the knowledge into your mind. It is potent enough to elevate a normal unicorn to a level above some of us alicorns, but is powerfully addictive. It relies on, not true magic, but the life blood of a creature, be it the caster, or, if the opportunity arises, an enemy that the caster has injured."

"Blood magic…" Twilight's eyes went wide as she grasped the full implications of what Celestia was giving her. The power to drain the life out of the blood was so taboo that even the most heinous criminals wouldn't dare to touch it. It was one of three crimes punishable by death, and the only one where there was no possibility of grace. This was a law that Celestia herself was not above, and even its practice was enough to damn a pony. The purple princess swallowed hard, but knew her duty was to protect the ponies she held dear. "I'm ready…"

"Good. Remember the severity of this burden, and do not ever take it lightly. We must protect Equestria from whatever threatens her." Celestia put her horn to Twilight's, and the knowledge of the blackest art seeped in like a leech into an open wound.

Present Day…

No, there were other alternatives, her magic was running low, but most of the ponies would be out soon, and all she had to do was keep them shielded and the serpents distracted until they fled. She had seen some of her friends escorting groups away, so they should be gone soon. A prismatic flash distracted her for a half a moment, but with the number of spells she was maintaining at once, that was all it took. The shields flickered for a brief instant, and Twilight heard screaming as the constant barrage of fire rained through, the shields now trapping the ponies inside the bubbles that had been being hit at the time with the fire that ate the ground they stood on. There was a crunch above her, drawing her attention up. There, she saw a bloody cyan hoof hanging from the mouth of one of the serpents, which then, to her horror, tilted its head back to bring the outlier in.

Her hovering faltered as her magical reserves began to deplete to almost nothing, not even allowing her basic sustained flight. The shields all flickered, and the wind died, all was screaming and burning and roaring, but Twilight couldn't hear any of it as she watched that hoof slide out of sight.

"No! This can't happen, I won't let it!" She brought her horn down and her foreleg up, and gashed herself. She called on the magic of life itself to do what it was never meant to do. To cause death. She reached forward with a red tendril of energy, grabbing the bloody mouthed serpent by the jaw and pulling down. The joint came loose as she fed the tendril further in, ripping it open like a knife until a rainbow maned Pegasus dropped from its guts. Not wasting a breath, Twilight tugged at the fleeting life in the blood of the dying serpent, and pulled it into more deadly tendrils of bright crimson that streaked across the sky to strike serpent after serpent. Some had their wings ripped to shreds, and others were torn in half, but all of them fell helplessly as the Alicorn of Friendship was held in the grasp of the Blood Mage's Lust. She raged at those that dared burn the town that had adopted her, that dared hurt her friends, that DARED to take those she loved away from her!

Just as quickly as it had come on, Twilight realized what she had done, what she was still doing, and she stopped her massacre of the serpents, allowing them to make their fearful escape, and turned her attention to helping those in need. The tendrils swooped down, choking out fires and clearing rubble almost instantaneously. She caused the life energy to seep into the injured, restoring their strength and knitting their wounds, though nothing could be done for those that had already passed. Tears streamed down her face as she recognized almost all of her friends among the wounded. She knew that the healing of Blood Magic was a temporary fix, and that it wouldn't restore enough to get those like Rainbow any more than conscious and stable, but it was something. It also made up for what she had done, and what she had allowed to happen by hesitating so long. They had been relying on her to protect them, and she had almost failed. She looked down at the grey Pegasus colt below her. No, she hadfailed. And she had broken the oldest law in the process.

She landed solemnly, and looked around. Rainbow was trying to stand, but her leg was bent at an odd angle, the bone visible through the bite mark that proved she had seen the belly of a beast. Despite her worn appearance, she attempted a smile at her friend, "Hey, egghead. Thanks for the save. That was you, right? I don't think anypony else could have managed to rip that sucker open to pull me out like that. Wicked cool, by the way, remind me not to get on yourbad side." She tried to laugh, but coughed up a little blood instead, "Anyway, did we win? Are they gone?"

Tears began rolling down Twilight's cheeks as she gestured around her at the burning houses and the gory remains of the mutilated serpents, "Look around, Rainbow. Does it look like we won?"

Rainbow looked closely, the smile slipping away before she stared intensely back at Twilight, "Look, Twi, these are just buildings. Just rock and wood and stuff, that's not that big a deal. I mean, sure, there's some stuff in there that we can't get back, but nothing that really matters at the end of the day. Cause when it really comes down to it, all that matters is us. How many did we lose? If most of us lived to talk about it, then that's a win in my book. And it looks like you racked up quite the count for them, too. Why didn't you pull that tentacle thing out from under your wings at the start? That was pretty rockin, from what I saw before I took that little nap after being a temporary breath mint."

Twilight looked back down to her friend and licked her lips, "I…"

"Please, Princess." The Princess in question looked up to see one of her personal guards staring at her with tears in his eyes. His name was Solid Foundation, and he made models on the side. She remembered that he had said that he had two fillies, twins. Their mother had passed in the line of duty, and he had taken the assignment to stay close to them. And right then, he was staring at her as though she had just stabbed him in the gut, "Please, Princess, tell me that that wasn't what I thought it was. Tell me it was anything else. I swear I'll believe you. Just… Tell me it wasn't what it looked like."

Twilight's tears increased, "I can't." One of the last remaining tendrils of magic snaked forward and solidified into a rope to bind and silence Solid, "Rainbow Dash, I have to leave. Tell everypony that I'm sorry." And with that, the few tendrils of power remaining flew together to swirl around her before vanishing in a red mist, leaving Rainbow Dash yelling at empty air.