Isopropylbenzylamine is the first thing that comes to mind. It is a precursor to the manufacturing of some drugs used by pharmaceutical companies. It's cheap and easy to get. The DEA is getting wise however. Mind you, it is a structural isomer of methamphetamine. I know it gets crazier. read more
If I understand your question, without knowing specifics, the fake “crystal” that people smoke would be what is known as bathtub crank or shake n bake. And the ingredients that are in it are extremely toxic, to say the least. read more