"O C'mon All Ye Faithful", titled onscreen as "A Derren Brown Christmas", is the tenth and eleventh episodes of the thirty-sixth season of the American animated television series The Simpsons, and the 778th and 779th episodes overall. The episodes were the first to be released exclusively on the streaming service Disney+ and were released on December 17, 2024. The episodes were written by Carolyn Omine and directed by Debbie Bruce Mahan and Matthew Faughnan.

In this episode, Derren Brown accidentally hypnotizes Homer into believing he is Santa Claus while Ned questions his faith in God. Illusionist Derren Brown, musician Patti LaBelle, and a cappella group Pentatonix appeared as themselves. The episode received positive reviews.