Sacred Haven of Debauchery

I hope the "majority of cases" where you are absolutely certain you are right don't happen too often.

This is 100500% an introductory word.

Well, he really messed up, didn't he?

And this is like an idiom, although I'm not entirely sure.
More precisely, it's a modified idiom, or something similar. In my opinion, the comma isn't needed.

Added 1 minute ago
P.S. Lock and Vis, just each of you explain your reasoning. Lock, if you're sure you're right, is it so difficult for you to justify it?