Solid. Could use a little fleshing out. Maybe the preserved skin of a LIVING troll would be best - after all I doubt the flesh would be doing much regenerating if the troll is flayed after death. I like the mention of alchemy, but it could use a little fleshing out - I want to know more about the process of making it. Aside from a little acid, you didn't say enough about it to quench my curiousity. Could be something good - perhaps I'll come back to it once you extrapolate?