I should clarify that the burns to death part is actually quite slow once you get to higher difficulties, and stops once you're more than a few screens away.
The set dungeon is actually easier than it used to be, because they changed the stupid simultaneous burning requirement that was the real problem with it- it's burn OR kill now. Took me 2 tries to get mastery this season, as opposed to about 20 when I did it the first time. :)