Remlari's Madness

In a world of magic and peace, people use magic daily to help themselves in their daily life. They churn butter with magic, walk their pets with magic, ignite fires for cooking. The land is filled with happiness. That is, until one day. A magic user thinks the unthinkable. "What if I use my magic for something that doesn't help me, but hurts others?" It changes everything. This wizard ended up honing his skills far too well, and became the most powerful in the world, and everything else crumbled. The sky is permanently dark red due to the extreme ash and fire. Grass and plants wither, people turn into large skin masses of teeth and eyeballs and appendages, and the smell of death sweeps the land. Only one person remains, a person who was isolated in a prison the entire time. Weak, but immortal. They have been placed inside a cell for 400 years and forgotten about. But one day, the bars corrode, and now they must see how much the world has changed since they were put in.