Sam Littlefield has been cast as Mouse in CW's Batwoman, according to Deadline. Described as a "dynamic figure... working for the Alice in Wonderland gang," Mouse is reportedly a recurring role in the series. In Batwoman, Rachel Skarsten plays Alice - a Lewis Carroll homage, of course.
In comic book continuity, there is a Alice in Wonderland gang member known as Dormouse, who piloted their flying teapot.
Littlefield is best known for playing Leland Schiller in CW's short-lived 2015 show The Messengers. Since then, the actor has had small roles in NCIS and The Leftovers.
Batwoman is scheduled to debut October 6 - you can read an advance review of the first episode here.