Mark Evanier knows a lot of cool people. Here's yet another one he recently posted about: a singer/impressionist out of New York, Christine Pedi, who apparently closes her Christmas cabaret show, her "Holly Jolly Christmas Folly," with "The 12 Days of Christmas"--a version in which she sings each verse as a different person, called out by the audience. The video quality is not great--and listen close otherwise you won't be able to hear the name the audience has called out. And it probably helps if you know a bit of theatre. But this is so good it must be witchcraft. Seriously.
(Also, bear in mind this is two videos stuck together--and I don't know if the second half was edited weird or if it's by design, but she's suddenly doing Liza and Judy Garland in between halves of "12 Days." So keep your ears open.)
You can find more info about Christine at her official site.