Portia Gloomgusset was an eccentric local witch known mostly for minor cures, frizzy hair, and a deeply questionable fashion sense. Her deepest ambition was to care for and shelter large numbers of cats. She built them little shelters, crafted elaborate scratching posts, and had collected entire crates of catnip-scented toys, happily toddling around her hut in a hat which was an extraordinary shade of purple. The problem was, cats were scarce in that part of the country due to an offhand curse pronounced by Kamu the Mighty some decades past. (It turns out he was also Kamu the Mighty Allergic.) So dear addled Portia set about trying to make her own cats from other, more plentiful animals nearby, most of which were newts, frogs, and other non-allergenic amphibians.
For the most part, her limited sorcery succeeded only in creating some very furry newts, the occasional standoffish frog, and a moody salamander with a tendency to scratch. However, once in a while Portia's erratic sorcery would produce something more significant.
The Thunder Newts were one such accidental product of Portia's experiments. She was hopeful at first that the periodic soft rumbling they produced was some sort of purring, but soon realized to her disappointment that the Newts were just thundering. She was uninterested in her creations' ability to generate small bolts of lightning and miniature storm clouds, and let them wander away, while she got back to the business of trying to put pointy ears on a toad.