Crocodile (It's Behind You!)

Like Captain Hook, a large, fearsome crocodile appeared as a fictional character in at least one common panto.

As a result, an old crocodile costume was one of the props stored in the understage area of one theatre where the Thirteenth Doctor, Yasmin Khan and Dan Lewis came to see Cinderella. After the Doctor used a link from Spacebook in an effort to bring "the magic of pantomime" to the performance, the props and costumes were replaced with real versions, "snatched" from other places and realms; as a result a real version of the crocodile was summoned. It attacked the group alongside several other pantomime villains, and, grabbing a stick, Yaz had keep it at bay while the Doctor found a way to fix things, managing to do so by wedging the stick between its jaws. After the Doctor found a Genie's magic lamp among the props, she was able use one of her three wishes to "wish" her friends safe, resulting in all the pantomime characters being returned to whence they came. (COMIC: It's Behind You!)

Behind the scenes
The crocodile pursuing Captain Hook is a character in J. M. Barrie's play and novel Peter Pan; or, the Boy Who Wouldn't Grow Up, as well as miscellaneous adaptations thereof.

The Genie mentions in It's Behind You! that what the Doctor did "snatched" him from another realm. It is not clear if this was specific to the Genie, or if all the pantomime characters were summoned from parallel worlds as well, rather than being native to the Doctor's universe.