I was thinking about the particulars of season 3, particularly the Mayor.  Sorry if this sounds dumb, but I was trying to get a few things straight in my head.  So he made a deal that he would get to become a demon in 100 years time, if he built a town on the Hellmouth, right?  I'm assuming that he could be killed in these 100 years, you know, if someone killed him, but that he wouldn't get old and die.  Do you think the Invulnerability ritual was a necessary step in the Ascension, or just something he thought it prudent to do, since things were heating up?  And the eating of the bug things WAS an Ascension step, right?  If he had been prevented from eating them, do you think he still would have been able to turn into the snake?

Yup, he had to eat those spiders as part of the Ascension., and yep, no aging.

That was me. Wasn't signed in.

The spiders was definitely part of the Ascension because he remarked how his organs were changing, merging, and that the transformation into the demon would begin soon. I think the invulnerability was not a step toward the Ascension, just something the Mayor had in his list of things to do building up to the big finale. It could have just been something he thought would help, and he did it a while before graduation. Not sure.