Mrs. Mouse is reading "A Visit from St. Nicholas" to her brood when a cat tries to break in. The cat overhears them arguing about the existence of Santa, so he dresses up accordingly.
Acting
Billy Bletcher's gleefully menacing Santa-cat voice work

Director
Rudolf Ising
Trivia, insights & behind the scenes
This was Rudolf Ising's final cartoon for Harman-Ising before MGM poached him to launch their animation division, making this a weird historical bookmark.
Billy Bletcher later voiced Pegleg Pete and the Big Bad Wolf for Disney—this cat's Santa voice is basically a dry run for decades of cartoon villainy.