You won't like her when she's angry
It had already been a few hours the sun had set over the bustling city of Maretropolis. Even without the presence of any daylight, the entire city was wide awake. Ponies traveling from one place to another, meeting up with their loved ones or associates, spending the evening chatting, walking, or having a meal together. Even though they had heard the news about the former owner of a hair-care product company turning into a super-powered criminal, they were not about to let that get in the way of their enjoyment of a nice evening like this. The air was warm, there was not a cloud in the sky, and the full moon was shining as bright as a diamond. Needless to say, every single pony was spending quality time with one another and they would not have it any other way.
Well, ALMOST all of them.
Just a mile north to the heart of the city, there was a small animal hospital run by a mare who would much rather spend time with her patients than go out and socialize with other ponies. Her name was Spruce Spanner and she was one of the most brilliant minds in the entirety of Maretropolis. Most ponies would think that a scientist as smart as her had dedicated her life to finding new innovations in order to help those in need. They would be correct save for one little detail.
The ones she had chosen to help however she could were not ponies, but animals of every shape and size. It did not matter if the patient was a wild or domesticated animal. All that mattered was whether or not it needed help and if it did, then she would be more than happy to give aid with the very best of her abilities. It also helped that she preferred the company of animals over the company of ponies due to her rather mild-mannered nature. In fact, her only pony friend in the whole city was her younger brother and trusted lab assistant, Brick Bones.
While he was also fairly introverted, he was, at the very least, willing to go around the city and socialize with other ponies. He also encouraged his elder sister to do the same from time to time, but she always said she was too busy with either a patient or a new invention. Speaking of inventions, she often occupied herself with building them in her personal laboratory so that she could better help her patients. These ranged from a serum that could increase the strength of any type of bone to a gun that could fire cryogenic beams and destroy any type of cancer cells.
In fact, she had been working for a whole week on building a machine that could potentially put all the previous inventions to shame. It was so big and complex that both its construction and her treatment of the patients had caused her to lose sleep more than once. Also, pretty much the only thing she was consuming during that period of time was black coffee. Despite these harsh circumstances, however, she was finally beginning to relax due to the fact that the project was nearing its completion.
It was just before midnight when Brick entered the hospital. All the nurses had already left and the entire building, save for the patients in the intensive care, was empty as a result. While Brick did know that he had no shift that day, he still wanted to check up on his sister and make sure that she did not exhaust herself to the point of collapsing on the floor.
Spruce may be older than him, but as her brother, it was his job to keep her out of harm's way. With that in mind, the tall Pegasus with pale gold mane and pale aquamarine coat promptly made his away across the hospital and entered the lab.
When he finally arrived, he found that most of the lab was exactly as he left it the previous day. All the equipment and chemicals were in their proper places, there was a significant amount of dust and machine parts on the floor, the computers were lit up like firecrackers, and Spruce herself was taking sips from what was quite possibly the three hundredth cup of coffee that week. The only noticeable changes were the significant progress on the machine's completion, the increased amount of dirt on Spruce's white lab coat and light grey body coat, the increased level of messiness of her chocolate brown mane, and the increased number of lines around her pale gold eyes.
Brick let out a deep sigh and asked, "Don't you ever go home or even outside for that matter? You do know that I could take over the construction duty any time you want, right?"
"I do, I do! ", replied Spruce before loudly yawning. "It's just that I didn't want to make you tired with several overtime hours and interrupt your break. Besides, I'm putting some finishing touches on the device and they are very delicate."
"So, it's finally ready, huh?", Brick remarked while gazing with his brilliant magenta eyes at the machine, which looked like a rotary laser cannon shaped like a syringe equipped with a barrel containing a few dozen smaller differently colored barrels, just like a minigun. "I sure hope this is worth all of that hard work and all those sleepless nights."
"Oh, it definitely is!", Spruce enthusiastically declared right after finishing her cup of coffee. "It's pretty much going to revolutionize the animal healthcare across the country. Maybe even across the entire world. Just imagine. With it, we'll be able to cause cellular regeneration in every species of animal on the planet. Doesn't that sound amazing?"
In response, Brick gave her a confused look and asked, "Now, hold on there, sis. I know this has been your childhood dream and all, but don't you think you're a bit too obsessed with it? I mean, when are you planning to start running the tests, anyway?"
Spruce let out a nervous chuckle and replied, "Well, this might sound a little crazy, but I've actually been thinking about testing it either tonight or tomorrow morning. Now that you're here, maybe we can run a quick test right now, instead. So, uh, what do you say?"
Upon hearing that, Brick's facial expression changed from confused to extremely shocked, and he exclaimed, "Alright, time out! Has excessive amount of black coffee scrambled your brain, somehow? You don't even know if this thing will ever work. You should double-check your calculations before running any test whatsoever. I think we both know that a single miscalculation can always ruin everything."
"No need", Spruce confidently declared. "I've been working on this device for the entire week. I've checked and re-checked every single calculation at least a hundred times. Plus, I've thought about and analyzed every possible scenario dozens of times, and right now, I can safely say that there is no way the machine will fall apart or blow up after we turn it on. Now, please, bring here the elderly patient who is missing one his limbs. I've been waiting a very long time to finally see the fruits of our labor and I assume you feel exactly the same."
Brick responded by letting out another deep sigh and said, "Fine, but I do have to remind you that you're barely standing straight and there are dozens of tired lines around your eyes at the moment. We'll run just one test and then, you're going straight home. First thing tomorrow morning, we are going to have a serious talk about your habits and social isolation problems. Understand?"
Spruce loudly groaned and said, "Whatever you say, little bro. Now, could you please hurry up and bring me the patient already? We're so very close to making a dream come true and we simply cannot afford to waste any more precious time!"
This prompted Brick to swiftly exit the lab and during his absence, Spruce pressed a few buttons on the machine in order to activate it. As soon as she did, the whole thing lit up like firecrackers and began to give off a strange humming sound, which Spruce took as a sign of the machine's activation and a big smile appeared on her face, as a result.
A couple minutes later, Brick re-entered the lab while holding in his left hoof a snow white rabbit, which was, indeed, missing one of its legs. He placed the rabbit right in front of the machine and took several steps backwards, while Spruce aimed the device directly at the patient and pushed one final button to fire the regeneration beam. It immediately struck the rabbit and surrounded it with a strange purple energy. Since it was too bright to see, both Spruce and Brick were covering their eyes during the whole process. It lasted for nearly half a minute before the beam died down and the ponies looked down to see exactly what had happened.
Once they did, they were both amazed by what had transpired. The rabbit's missing limb was no longer missing. In fact, it had actually grown an entire new limb due to the beam's energy. It took a moment for the rabbit to adjust to this new development, but as soon as it did, it was hopping around the lab without even the slightest sign of limping.
The scene made Spruce so happy that she shed a few tears of joy. grabbed the rabbit, and gave it the biggest hug she had ever given in her life while exclaiming, "Yes! Yes! YES! It works! It really, really works! We did it! We actually did it! From now on, no animal on this planet will ever get sick or lose a body part like old Betty here. She may have had to walk on only three legs for many years, but thanks to our new miracle worker of an invention, she'll be able to spend the rest of her remaining few days hopping like a normal bunny again."
Right after saying all that, she put the rabbit on the floor again in order to let the recovered animal hop around a little bit longer. Then, Brick came near her and placed his left hoof on her right shoulder before softly remarking, "You're right. We've accomplished something truly wonderful and the whole world will benefit from it. However, how about we leave that business for tomorrow and go home already? You've worked so very hard on this and you definitely deserve a good long rest. We're still going to talk about your isolation problems in the morning, though."
Spruce responded by first letting out a heavy sigh and then, giving her brother a nod of approval. She promptly picked up the rabbit and both ponies were just about to head out from the lab when suddenly, they heard a strange sound from behind. They turned around, and were instantly horrified to see a number of small purple-colored electric sparks appearing on the machine and some black smoke rising from it.
"What the heck is going on?!", frightfully asked Brick. "I thought you said there was no way it could blow up or fall apart!"
"I did!", Spruce replied with an equal amount of fright. "I-I have no idea what's happening! Maybe, there was something wrong with one of my calculations."
Brick then groaned with pure frustration and exclaimed, "I knew it! Your eyes were so tired that you couldn't tell the difference between two numbers. All of this could've been avoided if you just listened to me and got out of this darn lab once in a while!"
"There is no time to argue! If we can't stop this energy leak, the resulting explosion could demolish at least half the building and since the power source is radioactive, there could be fallout with a quarter mile radius!", shouted Spruce before handing the rabbit she was holding with her left hoof to Brick. "Here. Take Betty and get all the patients out of here while I stop a potential calamity from happening. Get as far away from here as you can. I'll find you once I'm done here."
"What? Are you crazy?!", asked a panicking Brick. "I am not letting you stay here and blow up with the building! Come with me right now and we'll fig- OW!"
Spruce immediately grabbed him by the mane and sternly explained, "Listen me very carefully! DOZENS of lives will be lost unless you do EXACTLY as I say! You may not value them as much as pony lives, but I certainly do and I'm willing to do ANYTHING in order to save them! Besides, this is MY mess and I'm the one who should clean it up. Now, GO!"
Inspired by his sister's unusually assertive tone, Brick determinedly nodded as soon as she released his mane. He then grabbed the rabbit, exited the lab, and began running across the hospital while releasing every single animal from their cages and leading them towards the exit. Meanwhile, Spruce was working as hard as she could in order to fix the machine (or, at least, stop it from exploding). Even though she pushed several buttons and tightened some loose screws, neither the sparks nor the smoke ceased to exist. Finally, after exhausting all other options, she resorted to removing all the panels and attempting to fix the problem from the inside. Despite the clear danger of the radiation emanating from the machine's power source, she quickly realized that there was no time to put on a radiation suit and proceeded to put her plan in motion.
Once all the panels were removed, she saw that the source of the problem was a wire right next to the power source that had short-circuited. While she was repairing that wire, however, she suddenly began coughing and by the time she succeeded in fixing the wire, her coughs had become extremely violent. On top of that, her entire body began convulsing and she felt a severe pain growing inside her. As she creamed in pure agony, her legs, head, chest, and back started to enlarge in size. Her eyes turned red and her teeth soon resembled that of a large carnivore. Even her screams began to sound more animalistic and her lab coat was being torn apart due to the overall transformation. By the time it stopped, Spruce was anything but a normal pony. Instead, she was now a hulking beast of a pony and both her mild-mannered personality and vast intelligence had been replaced with uncontrollable rage.
Brick had just about evacuated every single patient from the hospital when he heard screams and a banging sound coming from the direction of the lab. Fearing for his sister's safety, he began trotting towards it and once he reached there, he found something that terrified him to his core: a gigantic monster that looked very much like Spruce was tearing everything apart with its bare hooves while making loud noises that resembled those of a wild animal.
While he did think about going inside and confronting the creature, he eventually figured that it would be a terrible idea to do so as, in her current condition, Spruce could easily crush him into a million pieces with a single hit. Therefore, he decided to slowly walk back outside and notify the authorities, hoping that they would resolve the situation without an incident. He proceeded to do just that and was almost halfway to the exit when-
CRACK!
He accidentally stepped on and crushed a lone cockroach crawling on the floor. As soon as the monstrous Spruce heard that crushing sound, it stopped its rampage, turned its head towards Brick's location, and began growling like a lion upon noticing him. A panicking Brick whispered to himself, "Oh, shoot!", before falling down from the impact generated by the creature stomping on the ground and smashing the entire exterior of the lab (including windows and concrete walls) like nothing. Then, it trotted towards him with incredible speed and just a couple seconds later, it was standing right on top of him, growling as intensely as ever.
Brick let out a terrified scream as soon as it stopped and then, fearfully exclaimed, "Spruce, snap of out it! This is not you! Remember who you really are! PLEASE!"
In response, the creature simply unleashed an extremely loud roar onto him and both of his ears were nearly deafened as a result. By the time the roar stopped, he had officially run out of ideas on how to get out of this predicament. He was trapped both literally and figuratively. Moreover, he was sweating like there is no tomorrow and his heart was beating faster than ever before. He soon come to the realization that there was simply no reasoning with the monster looking down at him with immense ferocity. By just looking at its eyes, he deduced that it had every intention to end his life and that his demise would be coming in a matter of seconds.
Finally, he decided to accept his cruel fate and took a deep breath to prepare himself for the inevitable outcome. However, just before he closed his eyes, he said to the creature with a very soft tone, "If you're still in there, sis, then know that I'll always love you. You're so much stronger than this. Do not let it control you."
As soon as he finished his sentence, the monster let out another ear-deafening roar, ripped his head off with its mouth, and swallowed it whole. It then proceeded to consume the rest of the body before smashing through the ceiling with a single jump and landing just outside the hospital. Both the evacuated animals and nearby bystanders ran away in terror once they saw the creature and then, it began its rampage through the city by attacking the nearest building.
Author's Note
Thank you so much for reading. If this turns out to be a success, I might write origin stories for other Power Ponies in the near future. Have a great day and stay safe. 
