Which version is this based on?
Doing a little research on this I have found out there are supposedly FIVE versions of this story: three actually written by Twain and two posthumously edits by Albert Bigelow Paine (1916) and University of California (1982)
The three main versions Twain actually wrote are called 'Chronicle of Young Satan' (set in 1590 Austria, abandoned in mid scene), 'Schoolhouse Hill'/Hannibal (set in Hannibal with Huckleberry Finn and Tom Sawyer as Satan's (now called No. 44) companions, also incomplete), and 'No. 44, The Mysterious Stranger'/Print Shop (set in 1490 Austria and the only version to actually have an ending). (http://barney.gonzaga.edu/~kwillis/)
Thanks to modern scholarship it is now knows the 1916 was Paine trying to complete the 1590 Austria version with the 1490 Austria ending. Since this is set in the "Middle Ages" it clearly is using the No. 44, The Mysterious Stranger version but is it what Twain wrote or what University of California had come out as the definitive version?