I sort of wonder if this is the movie Pegg and Frost should have been making, rather than Paul:
Mashing up stoner comedy and fantasy is a good idea, and even sort of traditional, isn't it? The trailer did remind me that one of the impacts of being a) young and b) almost completely isolated from non-book pop culture in the 1980s was that I totally missed the cheesy, pre-advances-in-special-effects, live-action fantasy movies of the era. I did see Labyrinth in college, and though I get the humor in David Bowie's terrifying codpiece, I'm not sure I truly appreciated it, and of course I've seen The Princess Bride. Is it worth digging into the tradition further? Any suggestions about where to start?