This is part of a series of notes written by Professor Rosewood, It's mostly me trying to actually post my writings/world buildy shit publicly. Lemme know what you think! comments more than welcome!

-Obv. this isn't official canon, so take with salt but it's little details like this that I like to think about.

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-File Access Granted-

Professor Rosewood's Notes; Mega Evolution and Kalosite

"Mega stones were first used roughly 3000 years ago in the Kalos region to induce an instantaneous Mega Evolution on many species of pokemon, however these relics are refined versions of a mineral known as Kalosite. Most depictions of mega stones are seen as purely combative, used for war..and from some of my studies, prolonged use of mega stones is..Painful. Houndoom is a prime example of this, as parts of it's body get so hot it becomes harmful to itself. It's theorized by Professor Sycamore of Kalos that a Mega Stone's violent effects were caused by rush, imperfect refinement during time of war."

"Returning to Kalosite; It possesses a radioactive quality that only effects Pokemon. Prolonged exposure will cause the same "Mega Evolution" changes that a Megastone would, but gradually over time. This is not only beneficial, but permanent, and without any harm due to a lack of a sudden increase in size or power. Many pokemon currently exist who are permanently in a state of "Mega Evolution" due to Kalosite exposure."

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Shorter one, kinda just something as an idea/reasoning as to how some pokemon remain mega evolved permanently.

Ferilis Region + Professor Rosewood; me
Pokemon + Mega Evolution; Pokemon Company, Gamefreak, Nintendo, Creatures inc