Trying to make backstory for character I've had in head for while. Just trying to decide where Am goes from here, how power works.

Online story below:
Ambrose trudged along, hands in his pockets, hood pulled up tight against the cold as music blared through his ears. He appreciated the space, though his legs were weary from standing all day, his throat raw from talking and taking orders. True, this was the long way home, cutting through the “park”, but it certainly beat moving through the city centre, with its drunken crowds and Saturday night parties. Safer too- sure the park was a wasteland, a section of city upturned twenty years ago, and simply scattered with trees, turf and grass rather than rebuild the great swathe.
Some buildings still stood in the darkness, hollow, empty places scrawled with graffiti, picked clean for materials, and occasionally with childish slides or skater ramps constructed alongside them. They were empty at this time, but Am didn’t mind those guys so much, he got along, even if every attempt on a board left him flat on his ass.
The path curved ahead as gravel scrunched beneath his boots, swinging into the well-lit centre of the park where the memorial- a polished ivory obelisk- towered amongst a ring of benches. His luck proved true again, the park was well and truly abandoned, lacking the usual smattering of homeless sleepers or morbid romantics that the benches usually attracted. Probably a result of the armrests some twat had installed, he decided with a glance, before pausing as a purple glint caught his eye.
A small box lay on the nearest bench, a round container wrapped in shimmering violet. No, an Easter egg maybe? Ambrose frowned and plucked his earphones out, his curiosity piqued. Easter was still a month away, but this certainly reminded him of a Fadbury’s egg. Pale eyes flicked back and forth around the terrace, taking in the fifteen foot high monolith with flowers scattered around the base. Was this meant to be in memory of someone? No, who left a chocolate egg at a memorial? More likely this was just someone with a short memory. Or did someone want to give a stranger a sweet, a little good deed?
He liked that idea best and snatched it up in a smooth motion.
Crasssch!
The egg disintegrated in a shower of violet dust, his hand sweeping through it as if made of sand.
“The heck?” Ambrose gasped, taking a step back as the purple dust spread in a small cloud, sparkling in the streetlights. Definitely not a chocolate egg, not wrapped up, but what was it then? A superfragile sculpture? Some kind of tech? Or supernatural device?
His spine shivered at the thought and he span on the spot, unaware of the pale colouring dying his hands. What if there was someone out there? A monster, a brute, a threat? The glare of the lights made the surrounding darkness nigh impenetrable, though still some overgrown rubble peaked its head. Rubble from the Ragnarok of 03.
He hurried away. Whatever that thing was, it was best to get a safe distance, and the Park’s sheer scale was only a reminder of how great that distance might need to be. Maybe that was a relic from the battle, some orb left by a villain, or a weapon of a hero. A power source?
Ambrose shuddered, pulling his hoodie tight around himself. He could feel the terror turning in his heart, sending it beating a samba through his body, making his skin feel rough, clammy and tight. He just wanted to get home. Get to bed. Get these aching shoes off. Maybe play a few rounds on the computer. And lock the doors. Shaun was away for the weekend with his family, it was just him, just him and anything that wanted to chase down an egg-smasher.
The thoughts filled his mind with worry even as an urgent warmth filled his body. That was to be expected after all, he was moving at a brisker pace, even if the warmth blinded him to the sliver of flesh his hoodie now slowed as it crept up. It seemed smaller on his figure now, as if shrunk in the wash, but instead it slower crept higher, clinging to his flesh tighter as his height increased and bones shifted. Jean legs rose to reveal ankles, and held closer to legs that slowly lengthened and thickened in a peculiar way.
A patch of steam puffed from his lungs, and Ambrose blinked, feeling… warm. No, hot? A small smile crept across his face as he moved his arms, savouring the sudden comfort swelling within, as if he had just finished a good hot chocolate from the café.
“What the heck?!” A hoarse cry rose as his arms crossed his chest, feeling some bump as if in a pocket, but the bumps felt the pressure too, and felt just as warm. His eyes widened as he halted beneath a street lamp, stretching his hands out in disbelief. They were purple now. Deeper in some areas, while others retained a normal tone, but certainly dyed by the dust, and further up the arm than had even hit that egg. No, why were his arms even showing, this jumper was supposed to be loose, and yet it felt tight, pulled across his shoulders and chest.
His shoes felt tight too, now pushed against by the warm flesh within, long ankles dyed violet, revealed in the orange light. Yes, he could definitely feel it now, the temperature was rising, and with it came a sense of comfort, and confidence and cosiness, like a hot water bottle filling his innards. And pushing. Pressure built and pushed his body, making it swell and grow, fill up the confines of his clothes and push beyond there. Steam jetted out with every breath as he panted, as if to recover from a winding that had never came, chest heaving up and down uncomfortably.
Ambrose shook his head and gritted his teeth, torn as the heat filled him and built. Part of him wanted to run home, back to the flat, while another wanted to rush back down the path, search for some sort of antidote. Or phone somebody?
His body wasn’t moving though. Maybe it was shock, maybe it was the power filling him, making his hair seem to crackle with energy, but even so he stood in place, feeling the changes almost accelerate in response to the boiling power. His skin was crawling, overrun by violet taint that covered him, even as a pressure built at his heat. His shoulders rolled and he struggled, tugging the hood from his skull before it strangled him. Something tore in the panic but he couldn’t care, his hands were flying to the zip, only to brush against something more.
No. He fell to his knees as a tearing noise came and sudden relief came from his shoes, where black talons were tearing through the canvas. A stretch highlighted the now more defined legs, firm under steamingly tight jeans, even as the shoes gave way completely to scales and claws that would have seemed to fit better on a dinosaur than a human boy.
His hands sported the same he saw, pushing them against the ground, slender scaly fingers topped by dark sharp nails and Ambrose struggled up onto hands and feet. He had to get up. Do something. Surely?
Hot. Burning heat blanketed through the being again, shooting down his spine and then continuing onwards. Underwear and jeans burst as a powerful tendril of flesh fired like a firework from the lifted rear. Longer and longer it stretched, like an amethyst spike several metres long and burning with the same vitality as the rest of his flesh. An instant later it switched to writhing, newly formed muscles twitching and swinging with a sudden power, and Ambrose lurched backwards with the weight, powerful thighs cleaving the remaining jeans along the seams so that a bare and surprisingly ample rear came to rest upon the gravelly path.
Smoke billowed now as Ambrose struggled to blink. He was tailed and bare legged now, and yet an urgent search confirmed fears he had never known before. Something was certainly missing, and it barely took a millisecond for her clawed fingers to fly to her chest. Large firm lumps greeted the palms, wrapped up tightly in fabric that threatened to split with every breath. Or breast, that was certainly the word, Ambrose noted, before another wave of heat spread through his- or now, her- whole being.
This one burned, properly, actually burning, sending what felt like cleansing flame throughout the violet creatures body. Muscles and bones bugled and stretched once more, magic fuelled the unnatural growth and sending the poor jumper finally splitting into tatters as twin, pale pink orbs bounced, joyfully free of their confines. Ambrose grasped them unfamiliarly, squirming in discomfort as her talons pushed into the path and her rear ploughed through the gravel, weighing far more than any she had seen. The strange tail whipped again, the sprouting white fur along the spine now revealed in its thick glory, and she tensed, feeling her body spread outwards ever farther. Her face felt strange, pale white hair tickled her cheeks, and a wandering hand found a rounded snout in place of his old pointed nose.
The other dug into the ground as every muscle tensed, wide hips and smooth legs bending obediently to position the clawed feet, and her elongated tail gave a powerful wave that sent the new creature into a crouch. Too fast though, the sudden balance caught her off guard and flailing claws grabbed ahold of some nearby pole. Yes, there was a good support, narrow, but enough to help to catch her balance and slowly force herself upwards, claws scraping the metal all the way.
A spasm caught her off guard as her abdomen seized and chest heaved. The burning was almost too great now, and for a second the creature doubled over, as if to withdraw and shrink back down. Instead she exploded, bones creaking and muscles screaming as the sheer speed and strength. One taloned foot gouged a deep trench across the path as it spread from its compatriot, and boulders were sent flying by a reckless lash of the tail. Her back arched with a terrible snap, newfound assets bouncing with the sheer motion as her long neck seemed to clench and then release.
A golden gout of flames hurtled upwards from a fang filled maw, burning heat flowing and forcing its way from her being in a wondrous burst that fired many times her one body length into the night sky, filling it with flames and dancing sparks.
Then Ambrose forced her jaw closed and darkness swept back just as suddenly, leaving her be. Somehow that was a surprise as much as anything, hadn’t there been light during all of this? Had she shorted it out with that burst of flames?
No, the answer lay as crimson eyes fell on her hand, clenched tight around a slender metal pole with a bulb on the end. The streetlamp took a second for Ambrose to recognize, it seemed like just a walking stick now, barely the length of her violet legs, which could only mean that…

“Holy smokes, I’m gigantic.” She was above the level of the other streetlights on the path. Heck, her body was wider than the path she had wandered down a mere few minutes earlier, an amethyst colossus with a lean yet powerful body, monstrous hips and an extremely notable weight nestled on her rib cage. Looking down was like staring off the edge of a building, past great round floats and down legs that seemed like shapely tree trunks.
It was too much. Too hot. Too big. He found himself moving, legs shifting, the lamppost dropped idly, and yet she barely registered any of it, sinking into blackness.