New big dragon boy for my roster, this time with the ability to shift between a smaller form and a larger form, just read the story for context and hope you enjoy.

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Deyrus was born in a Draconic tribe in a land away from Equestria and it's own Dragon Lands.
He lived a relatively normal life until he and the rest of his generation started to grow into their adult forms, while he, however, remained small and young looking.
As the years went by, more and more dragons young and old started picking on him for his small stature, some even stating that he must have some genetic defect. Including the Patriarch of the tribe.

One morning, Deyrus woke up to find himself grown to a full adult, turns out he was simply an extremely late grower and just now no one would pick on him.
However as he talked around town, no one recognized him, only that he reminded them of that pathetic specimen Deyrus.
This as well as not even getting an apology from when he told them who he is infuriated Deyrus. Vowing to make them pay one day he left the tribe in a fit.

He decided that overthrowing the Patriarch and becoming the new ruler would be a good start, so he began looking into magical objects to give him the edge in a fight.
It was then he discovered a strange tome that when opened, pulled him into a fantasy world within itself.
It was there he saw that world's version of dragons, all of them were twice as large as the Patriarch and had unique powers to boot. He knew that's what he wanted to become, that'll make overthrowing the Patriarch easy as well as deter any uprisings from the rest.
He set out in this strange world, determined to find a way to become one of these dragons himself. Which was actually as easy said and done as the book, sensing his wants, crafted a journey to claim it and people to aid him in finding it.
Deyrus did not treat these people kindly, seeing them as mere illusions that the book created, simply objects that gave him information.

Eventually he found what he was searching for, the Dragon Guard, a three piece set that gave you the qualities of a dragon, even letting one fully transform into a dragon.
Deyrus without a second thought placed on each piece then and there.
But in his over eagerness, he failed to realized that the items held a curse,
The metals clung to his scales fusing them together with a searing pain these items would now be part of Deyrus's till he died, which wouldn't be too awful for him besides the pain never seemed to go away, spiking whenever the metals moved too much.

But with these in his possession, he now held the powers of an aquatic blue dragon, allowing him to swim much more effectively as well as breathe lightning instead of fire.
After some testing with the false people, he made his way to exit the book with a collection of items, but discovered that talking things out of the fantasy world seems to make them disappear. Happy to know the Dragon Guard remained as it's connected to him, he later discovers that holding them in a special bag allows him to take other items as well.

With his trump card, he stormed his old village, demanding a duel with the Patriarch, and after some verbal abuse from both sides, the Patriarch agreed thinking he would win easily.
But as soon as the battle began, Deyrus unleashed his new power, blind siding Patriarch with a form twice his size.
Deyrus, not giving him a single chance, shoved the Patriarch into his maw and swallowed him whole.
The rest of his tribe were forced to watch in horror as Deyrus proclaimed his victory, becoming the new Patriarch when his gut stopped churning.

With his new authority, he immediately abolished the title of Patriarch and redubbed himself as Lord Deyrus, taking some of the female dragons that once mocked him as his brides, creating a consort from them.
He now spends his days in luxury, either bedding with his wives or revisiting the fantasy world for both fun as well as discovering his items needed to be recharged every once on a while.
But also having tge tribe's warrior capture any intuders and foreigners to be offered to him for his own fun.