I know this is an odd subject, but apparently, Rabbeinu Ephraim ben Shimshon, one of the Tosafists, thought that Binyamin was a werewolf (Translation by Rabbi Slifkin on this post):
Another explanation: Benjamin was a “predatory wolf,” sometimes preying upon people. When it was time for him to change into a wolf, as it says, “Benjamin is a predatory wolf,” as long as he was with his father, he could rely upon a physician, and in that merit he did not change into a wolf. For thus it says, “And he shall leave his father and die” (Gen. 44:22)—namely, that when he separates from his father, and turns into a wolf with travelers, whoever finds him will kill him. (Rabbeinu Ephraim, commentary to Genesis 44:29)
There is a type of wolf that is called loup-garou (werewolf), which is a person that changes into a wolf. When it changes into a wolf, his feet emerge from between his shoulders. So too with Benjamin—“he dwells between the shoulders” (Deuteronomy 33:12). The solution for [dealing with] this wolf is that when it enters a house, and a person is frightened by it, he should take a firebrand and thrust it around, and he will not be harmed. So they would do in the Temple; each day, they would throw the ashes by the altar, as it is written, “and you shall place it by the altar” (Leviticus 6:3); and so is the norm with this person whose offspring turn into wolves, for a werewolf is born with teeth, which indicates that it is out to consume the world. Another explanation: a werewolf is born with teeth, to show that just as this is unusual, so too he will be different from other people. And likewise, Benjamin ate his mother, who died on his accord, as it is written, “And it was as her soul left her, for she was dying, and she called his name ‘the son of my affliction’ ” (Genesis 35:18). (Commentary to Genesis 35:27)
I know the Chida mentions this in the name of Rabbeinu Ephraim (Dvash Lefi, letter Zayin, 15-16):
There is a wolf called loupgarou (werewolf) and he is a man and changes into a wolf, and at the hour of his chaging to a wolf, his legs come out of his shoulders, so Binyamin "dwelleth between his shoulders."[...] Rabbeinu Ephraim z"l in his commentary to the Torah [...]
From here it sounds like the Chida understands this idea as being literally true (at least according to Rabbeinu Ephraim).
However, in the next paragraph he writes:
A wolf that turns into a man, even while he changes into a man, during every hour he has a tail, so was the strip of land that came out of the property of Binyamin and entered into the property of Yehudah and upon it was the Beit Hamikdash.[...]
From here it sounds like a parable, though. However, in Rabbeinu Ephraim's words it sounds like he literally thought Binyamin was a werewolf. I know some people would say that he was saying this based on the popular myths and beliefs of the time - and I can accept that about commentaries on werewolves in general. It's equally possible, in my opinion, that there may actually be such creatures - the Talmud and even the Tanach are filled with descriptions about fantastical creatures and demonic beings (such as shedim) - so I don't think it's too far-fetched to say that in the past, when the world was more spiritual, and such creatures were more widely-seen, wolf-monsters could've also been around.
However, I don't know how either of these explanations reconcile with Rabbeinu Ephraim's belief that Binyamin, of all people, was a werewolf (and that he ate his mother!). That just seems too extreme to me.
Does anyone have any explanation for this?