I know, there was once where he go this head split open and he healed up fine. Now, if they would have it where his germ phobia was key as in: "I can heal from anything, but if I got hit with influenza or anthrax, I'm screwed!" Then you see he knew despite his abilities he wasn't invincible. However, the Mayor really never had much an origin story, especially when the Hellmouth was revealed for what it was both in season 1 and season 7. It sounded like the Mayor was behind the true origins of the town since they found all the pictures of him and they basically just had him "assuming" the role of being descended from the Wilkins line. Then it was: "Ho, hum... that's not important." Other wise it sounds like the Master established the Hellmouth, bit off more than he could chew (pardon the pun) and then everyone just took advantage of it.
Then they plugged in that the Seers were corrupted people and then branded themselves, but they really never got that right. I mean if the First was non-corporal, how was he merging with Seers and Caleb and giving them "super powers" yet no one could put their hands on it. I'm still a fan of Joss Weadon, but he was trying to have it both ways and use cast members from Firefly when the show got cancelled. I mean all of sudden here were Adam Baldwin, Gena Torres and Nathan Fillion on his shows in the middle of their seasons or ready to be over in less than 8 episodes. It came off like: "Well, our show got cancelled, they need a paycheck so let me just throw them in here."
I brought up Snyder because after he was so happy that Buffy left at the end of season 2 after defeating Angel. It was making it look like he was really kind of like a main underling and knew about all the super natural stuff in Sunnydale. Then they back tracked on all of that with the demon spider box and even at the end, Wilkins eats him. They were trying to have it that Synder was this big anal reteptive person that he is ordering a 300 foot snake to give him quiet instead of: "I'm fucking out of here!" I felt Synder could have been used much more relevent instead of the: "I'm a school authority figure and it's my way or the highway" cliche.