The Elf and the Magic Key (1993)

It's Christmas Eve and Santa Claus has been kidnapped and is held for ransom: the kidnappers want all the toys for the children by 5 P.M. on Christmas Eve. Toby goes to Mrs. Buzzard for help, who gives Toby a magic key for a special door, in hopes it'll break the spell that has kept her trapped in the den beyond Santa's mailbox.