What's wrong with his face?

Its a clostridial bacterial infection, its anaerobic meaning it doesn't need oxygen to thrive. Dogs can get it from a deep puncture or something, not necessarily from anything metal, usually a week or 2 prior to showing symptoms. It can be treated if in early stages with ampicillin, tetracycline, or metronidazole. We have treated some with antitoxin but with mixed results because of it being derived from livestock (or human) antibodies so it doesnt always bind like it should. It may be wise to take him in to a vet asap, even if its not tetanus. Its not common for dogs to get tetanus, but since it lives just about anywhere including dirt, and with what looks to be like scratches on his face, who knows what he got in to. Wish the best for his recovery.