longest way round;

Monster Theory - Really great anthology to start with, especially the first reading, Jeffrey Jerome Cohen's famous "Monster Culture (Seven Theses)" which is a personal favorite

The Journal of the Fantastic in the Arts - A general SF/F journal, but there are definitely a lot of great monster theory and gothic horror readings sprinkled throughout. Consider taking a look at Veronica Hollinger's "The Vampire and/as Alien," the special issue on Dracula, and Faye J. Ringel's "Genetic Experimentation: Mad Scientists and the Beast," among others

Werewolf Histories edited by Willem Blécourt - Phenomenal anthology on werewolf scholarship, especially if you're interested in the connections between werewolves and witchcraft and/or witch trials in Early Modern Europe

Skin Shows: Gothic Horror and the Technology of Monsters by Jack Halberstam - Of interest to those who are interested in the connection between the gothic and gender (among other topics). Halberstam has written extensively on both

The Journal of Dracula Studies - Exactly what it sounds like.

Preternature: Critical and Historical Studies on the Preternatural - Another journal, which focuses on the connections between witchcraft and occultism, monsters, demonology, and the like.

Susan Stryker's "My Words to Victor Frankenstein Above the Village of Chamounix" - An absolutely landmark piece of writing on Frankenstein and the transgender (and in particular the transfeminine) experience; one of my favorite pieces of academic writing of all time.

Speaking of Monsters: A Teratological Anthology - Another solid monster theory anthology

Arts of Living on a Damaged Planet: Ghosts and Monsters of the Anthropocene - A really, really good anthology about the ecological gothic that I cannot recommend enough. As a known werewolf guy I especially like the piece "Wolf, or Homo homini lupus" by Carla Freccero

The Vampire Lectures by Lawrence Rickels - So many vampires

Monster Culture in the 21st Century: A Reader - Another anthology, I in particular recommend Rosalind Sibielski's "Gendering the Monster Within: Biological Essentialism, Sexual Difference, and Changing Symbolic Functions of the Monster in Popular Werewolf Texts" in this one.

"The Trans Legacy of Frankenstein" by Jolene Zigarovich - Definitely a good read if you enjoyed the Stryker piece earlier; it's a more general survey of the idea but might give you some ideas for further reading

TransGothic in Literature and Culture - A whole anthology of works on transgender identity and the gothic!

Twenty-First Century Gothic: An Edinburgh Companion - Not to be confused with the other similarly named anthology earlier, this one is on various modern perspectives on the gothic.

"Christians and Jews in the Twelfth Century Werewolf Renaissance" by David A. Shyovitz - Stand-alone article but really really interesting

Wonders and the Order of Nature: 1150-1750 by Lorraine Daston & Katherine Park - Incredible volume that gets into several different subjects surrounding the fantastical in the medieval and early modern eras, monsters among them. The same authors have written some other fantastic work, such as "Unnatural Conceptions: The Study of Monsters in Sixteenth- and Seventeenth-Century France and England" and I honestly would recommend any of their work.

Monster Anthropology: Ethnographic Explorations of Transforming Social Worlds Through Monsters - A more anthropology focused volume, I particularly like Rozanna Lilley's "Drawing in the Margins: My Son's Arsenal of Monsters—(Autistic) Imagination and the Cultural Capital of Childhood"

Marvels, Monsters, and Miracles: Studies in the Medieval and Early Modern Imaginations - Another anthology, this time with a historical perspective