Periodically, I'll get a notification that I can use the Enigma machine to determine the location of one of Riddler's hostages. This seems tied to the number of the Riddler challenges I've completed in the game so far.
What are the milestones I have to reach for each hostage room?
I'd also really like to bust the Riddler before I hang up my cape and cowl. What percentage of the challenges do I need to conquer before I can wrap this case up?
Catwoman also has some Riddler challenges associated with her - how do these factor in? Must I do them as well? Can I do some instead?