Yes, it's another link-post, taking a look at the existing material from a specific subject filter up through entry #82.
Before the rise of the concept of "genre fiction (a relatively recent phenomenon), a great deal of popular literature included fantastic elements -- whether the overtly fantastic, such as tales of magic an otherworlds, or fantastic elements that the storytellers and their audiences may have understood to be parts of their own reality. Here are a some of the publications covered by the Project that address literature (or ideas) that would be considered "fantastic" by today's standards. The majority of these come out of the tradition of medieval romance, which can easily be traced as the origin of large chunks of modern fantasy literature.
Amer, Sahar. 2008. Crossing Borders: Love Between Women in Medieval French and Arabic Literatures. University of Pennsylvania Press, Philadelphia. ISBN 978-0-8122-4087-0
The tale of Yde and Olive has the most overtly fantastic elements of the stories covered here, with the motifs of a magical sex-change or the direct intervention of Saint Michael in the form of a white stag (or both).
Brooten, Bernadette J. 1997. Love Between Women: Early Christian Responses to Female Homoeroticism. University of Chicago Press, Chicago. ISBN 0-226-07591-5
The magical love-spells covered by Brooten's research are "fantastic" in intent and imply a belief in the existence and effectiveness of magic.
Clover, Carol J. 1995. "Maiden Warriors and Other Sons" in Robert R. Edwards & Vickie Ziegler (eds). Matrons and Marginal Women in Medieval Society. The Boydell Press, Woodbridge.
To the extent that Clover's topic represents actual cultural practices, it does not necessarily represent a "fantastic" element, but the specific examples are drawn from adventurous tales from Norse and Germanic literature that include a wide variety of fantastic elements, including gods and monsters, enchanted swords and magical curses.
Donoghue, Emma. 2010. Inseparable: Desire Between Women in Literature. Alfred A. Knopf, New York. ISBN 978-0-307-27094-8
Only the first chapter of Donoghue's study covers significantly fantastic elements, covering tales of transformation and well as the ordinary fantasies of medieval romance with their fairies, amazons, and quests.
Hotchkiss, Valerie R. 1996. Clothes Make the Man: Female Cross Dressing in Medieval Europe. Garland Publishing, Inc., New York. ISBN 0-8153-3771-x
Again, it is largely the coverage in one chapter of medieval romances -- with their fantastic adventures and otherworldly settings -- that brings this publication into the fold.
Krueger, Roberta L. 1999. “Transforming Maidens: Singlewomen’s Stories in Marie de France’s Lais and Later French Courtly Narratives” in Bennett, Judith M. & Amy M. Froide eds. Singlewomen in the European Past 1250-1800. University of Pennsylvania Press, Philadelphia. ISBN 0-8122-1668-7
Another article looking specifically at medieval French romances, where maidens encounter otherworldly quests with the aid of supernatural mentors.
Pintabone, Diane T. “Ovid’s Iphis and Ianthe: When Girls Won’t Be Girls” in Rabinowitz, Nancy Sorkin & Lisa Auanger eds. 2002. Among Women: From the Homosocial to the Homoerotic in the Ancient World. University of Texas Press, Austin. ISBN 0-292-77113-4
A more detailed look at a fantastic transformation story.
Roche-Mahdi, Sarah. 1999. Silence. Michigan State University Press, Lansing. ISBN 0-87013-543-0
A cross-dressing heroine in an Arthurian adventure tale.
Sautman, Francesca Canadé. 2001. “What Can They Possibly Do Together? Queer Epic Performances in Tristan de Nanteuil” in Same Sex Love and Desire Among Women in the Middle Ages (ed. By Francesca Canadé Sautman & Pamela Sheingorn), Palgrave, New York.
More Arthurian adventures where gender disguise results in homoerotic encounters.
Vanita, Ruth. 2001. “’At All Times Near’: Love Between Women in Two Medieval Indian Devotional Texts” in Same Sex Love and Desire Among Women in the Middle Ages (ed. By Francesca Canadé Sautman & Pamela Sheingorn), Palgrave, New York.
The stories covered here often include elements of gods and heroes, with overtly fantastic elements such as magical female impregnation.