At Christmas time you must be sure to include the Festival of the Holidays entertainment in DCA. My favorite show is Viva Navidad! It’s such a vibrant exposition of how Navidad is celebrated by the Latin American culture & includes Donald plus the rest of the Three Caballeros as well as Mickey & Minnie appearing in cultural Latin dress along with ensembles of musicians and dancers. So well done.
There are also the Bell-Ringers that perform on Buena Vista St as well as many smaller live performers on stages set up around DCA that reflect all different holiday traditions of the reason, not just Christmas. And along the main walkway of DCA they’ll also have toy solider drummers that roam as well as some fun elves on stilts. So I guess I’m saying, don’t miss the Festival Ambiance in DCA because it livens up and adds so much to DCA that you don’t get when the holidays aren’t there. Even the spring Food & Wine festival (which does similar offerings) doesn’t have quite that same vibe as the Holidays festival.
If you’re at all into Character meets then in DCA they also have meets with the Three Caballeros and Mickey & Minnie in their cultural Latin dress meeting near where Viva Navidad is performed.
Also specific to the holiday season in DL, there’s a castle-lighting that’s beautiful (done 2x a day), both parks also have a tree-lighting at sunset-ish. And totally jumping on @Ms.BarbsWildRide’s recommendation of IASW after dark, you also need to watch the facade light-up with a little min-show of projections & music which also happens at Sunset but then repeats every so often throughout the night. I also could care less about IASW on a normal day (my kids love it so I ride it for them) but at Christmas it is probably one of my all-time favorites- only surpassed by Haunted Mansion Holiday (which is on the map but is a must-do & usually a repeat that we do at least 2-3x a trip that we take during the holiday season- last year my daughter requested it 9x on her trip with Mom & Dad and I think we were able to it get it at least 7-8x on our 2 days there).