I was going through the book to add some subclasses to a campaign, and there's something called "Stride the Inferno" under Exorcist clerics that I can't find anything about. Can I ask what it is?

That is a feature from an early iteration of the class that unfortunately didn't get removed from the feature list. I am working on a revision of the book so I'm going to add this to my notes to fix. Thank you for spotting it!