Jane Holloway was a 47 year old English teacher who was one day blessed from out of the blue with all of the arcane knowledge of the ages, which wasn't much. She could turn a stick into a snake, but had a great fear of snakes so she didn't do that. She could float, but not fully fly. She could tell the future, but never in a way that she understood when she did and she could make you have a bad day, or turn you into a toad. Overall she wasn't very talented with her gift, which was a blessing to the rest of the world, because real talent would have doomed us all. Instead Jane was sort of a paranormal custodian, she sort of did what magic bid her to do and didn't ask too many questions. A good magician was a servant of magic, and would sometimes take the credit for what happened if they wanted to seem powerful and mystic, but in reality it was the magic itself that did what it did, like surfing the best you could do was be along for the ride.
It was that very reason that she was called upon by the stone when Jon had wished for something interesting to happen. The magic in the stone could think of nothing more interesting than what would happen when a very ignorant and powerful witch was paired with someone like Sarah McMillian. So it sent her to Sarah, with the orders, "Do whatever she tells you", and just left it at that.
Jane Holloway showed up at Sarah's door with her best tricks up her sleeve, prepared to turn people into newts (knowing full well they'd get better) or turn lead into gold. She even brought her own lead. But shy and plain Sarah wasn't about revenge, she was about power. She wanted what she didn't have, popularity, beauty, power, Biff as a loyal boyfriend. And so Jane through out all her little tricks, dug deep, and gave Sarah what she wanted.
She did horrible things, stole whole lives from people, reducing them to nothing more than essence. It changed something in her, the depth of magic she had to touch, the lack of care she had to have for those girls, killed parts of her soul and she started to fall down the rabbit hole, becoming more and more unhinged. She watched as her creation, who was supposed to be all the best features of those lives she had taken became a bitchy evil queen of the school, an unstable menace. Still she was in too deep, the only way out was through, and so she forced Sarah to give back some of what she had taken to others, ruining yet more lives in the process. She felt a certain agreement with Sarah though, these were nobodies which she was helping form into somebodies, she was doing good by the evil she did, and she enjoyed it a little more this time around.
But too much had been taken, other magics had mixed with her own, she had lost control of it all and now she stood before those girls she had made, with the girl she had been sent to help reduced to a goo of essences. She looked at the bathtub, now half full of a pink slime which had once been Sarah McMillian, now nothing more than a magical afterbirth, and she felt like crying. Her cloths felt heavy on her, the world swelled in size, she didn't understand what was happening.
The door opened.