Mammy Christmas is the first of two Mrs Brown's Boys Christmas specials to be screened in December 2012.
Agnes is determined to land the role of the Virgin Mary in the Christmas Nativity, and has even written a letter to Father Quinn. Meanwhile, Trevor is home and Dermot and Maria are the proud parents of triplets, but then, Agnes is told by the new priest Father Damien that she cannot play Virgin Mary in the Nativity as there will not be one this year, so Agnes decides to write her own version. Agnes soon discovers that Father Damien has a problem with interfering mothers, and it soon emerges that he hasn't spoken to his own mother in five years. Agnes eventually forces Father Damien to reconcile with his mother. Also, Dermot and Buster decide to set up a Santa's Grotto in one of the empty shops. Dermot asks Buster to find someone fat and jolly to play the role of Santa, but Buster makes the mistake of asking Sharon McGoogan, and he enters the Brown kitchen battered and bleeding from the nose.
Meanwhile, Cathy discovers her mother has been reading her mail along with everyone elses and decides to get her own back by fooling her mother into thinking that she is being filmed for a television programme to find the best mother of the year, causing Agnes to behave untypically nice - until Winnie gives the game away. In Foley's, Buster tells Dermot he has gotten a chair for Santa for the grotto, but Dermot notices a man sitting behind Buster reading a newspaper with "Lord Mayor's Chair Stolen" splashed across the front page. They eventually decide Grandad is the ideal candidate to play Santa.
Also, Rory is to receive a hairdressing award, but when it becomes clear that boyfriend Dino won't be able to attend as there is only one ticket to the awards party, Rory chooses to give it a miss rather than go without Dino. In the final scene, Bono is too excited to sleep, so Agnes tells him a rhyme whilst playing her music box and Bono soon falls asleep and the episode ends.
- First appearance of Father Damien.
- Father Quinn is mentioned as having gone on a retreat.
- Bono now wears glasses.
At the beginning, when Agnes is stuck on the tree, behind her, you can see the star staying in place, however, the star was hanging upside down.