This article contains plot details from the latest book.
“All of her other abilities worked so effortlessly, she didn't understand why this one was such a struggle.”
—Narration, in Flashback
Inflictors are elves with the ability to inflict pain or other negative emotions on someone else, including elves and goblins. Sophie, however, can also inflict positive emotions, thanks to her alicorn inspired DNA. This ability has the capability to incapacitate others and is very rare. Because this ability can be dangerous, the Council monitor all Inflictors carefully.
Sophie describes seeing colors in her peripheral vision before she used this ability. When Bronte inflicted on her, she imagined a cold and painful sensation, showing that the feeling and effect of Inflicting may vary, depending on the Inflictor.
in Legacy, Sophie gets her abilities reset because the way that the Black Swan designed her inflicting is "malfunctioning." So Sophie does it, naturally, and then she can inflict properly again. Instead of taking out everyone around her when she inflicts, now she can direct her ability to one person, singling out the one who she wants. Sophie shows us this in the 8th book, by singling out Lady Gisela and inflicting on her specifically.
Sophie discovers this ability in the first book when she is with Dex in Paris. In a different book, she learns that she can inflict positive emotions as well as negative emotions because of her alicorn-inspired DNA. Sophie is also given back a memory in Legacy of her and Amy when they were younger, where she inflicts on Amy when her new ability gets triggered.