Apparently Jean de Meun, a medieval writer most famous for writing the continuation of The Romance of the Rose, wrote a fortune-telling manual that used 12-sided dice called The Dodechedron of Fortune. The Folger Library has an English-language version, including a sample page of fortunes. From reading the descriptions of other scholars, it looks like Jean based his 12 on the 12 signs of the zodiac.
No word yet on the location of Jean de Meun’s Monster Manual or Fiend Folio.
[For medieval scholars: Looks like it might be covered a bit in a special session at the International Congress on Medieval Studies this Friday at 1:30. Session 239, Fetzer 2040. I already had that marked in my own program even before I knew they were covering this.]