Percy Mortimer, also known as Phosphorus, is an escapee from the School.
Percy is tall and very thin, with dark brown skin, mostly white hair despite her apparent young age, and the typical purple eyes of School creations. Her right limbs and much of the right side of her face are dead, the bone visible and relevant muscular and nervous structures replaced with the telltale blue and black of her powers, including her right eye. She wears concealing clothing to hide this, making her stand out when the weather is hot.
Percy was born as Phosphorus of the Phantom Class, with abilities centered in the use of Electric Obscura to animate and manipulate dead tissue and dead bodies. She can puppet around corpses, generate an Electric Terrain that allows for the creation of enormous bone constructs, and even replicate the effects of Fossil revivification. Her powers require an immense caloric load, and she has developed a taste for sports drinks as a result.
During the Phantom Class breakout, she bought time for her fellow escapees, but ultimately fought Adelinde the Scythe, and was left for dead. She managed to put herself back together with her powers, and fled.
Eventually she ended up in Galar, running a pop-up stand reviving fossils and fixing phones.
Years of hiding out from the School have left Percy somewhat gruff and paranoid. Still, she's at her core a nice person, particularly to the kids who come to her to try and get dead Pokémon revived.
Percy is friends with Apple-A-Day after an unspecified incident, and despite her belief that they're a bit of an idiot has a soft spot for the hero.
After an initial misunderstanding, she is at the very least on cooperative terms with Lissa.
Percy is terrified of Adelinde after their last interaction, and hates her in equal measure. Adelinde finds this fundamentally amusing.