Yes, there are problems resulting from gangrene, but those seem to be highly localized at the injection site. So, systemic damage that has been reported would be things such as: pneumonia, blood poisoning, coronary artery burst, meningitis, rotting gums/tooth loss, bone infection and decayed structure of jaw & face, ulcers/sores on forehead and skull, rotting ears, lips, nose, liver and kidney problems, and some other gangrenous wounds.
So, what I've been looking for is obviously other chemicals in the drug that could destroy the tissues in such a way that could a)eventually cause gangrene (which is easy if you look at the localized damage) and b)something strong enough to eat away at the facial structure of a person. Anyway, I think now its just a matter of looking at various chemicals (as I've been doing) and looking at the toxicity of each. Apparently, after looking at toxicology of red phosphorous, that if it is contaminated with white phosphorous and chronically ingested, it will cause necrosis of the jaw bone. Then again people are also mixing this with Iodine which could form Hydriotic Acid (HI), so if that gets injected into the system, it would not be great either. So many substances that are possible considering each batch is different, but they all do have a few things in common.