I put the spoiler tag up there since I am not really following the main event. IMO Christmas time is not a good time to stage one of these when people are already spending their $$$ on presents, etc. But maybe that's just me
Having said that, this is a fun part of the event where you really don't have to know much to follow the story. Tony is still reacting over the death of Eddie Brock and how he played a role in it. Doom sort of randomly shows up to ask if he would mourn Doom as he is mourning Eddie Brock. This evolves into them discussing a few hypotheticals as to how that could possibly happen. One thing I have enjoyed about Cantwell's writing here, and in his Iron Man and recently concluded Doctor Doom series is he is very good at doing these kind of off the wall dialog scenes. IMO it gives a very human aspect to the characters, especially for Doom who many writers just resort to him making pronouncements and speeches. Larocca shows us a very detailed look at Tony's Extremis/Symbiote armor -- I'm not sure what else to call it. Later in the story, Doom reaalllly likes this armor and Tony tells him no chance of that happening.
While they are on the rooftop discussing how Tony would ever consider mourning Doom they see the approach of Santa in full regalia, sleigh and reindeer. That is they think it is until they get a closer look. Once again Cantwell shows some of his writing skills with the dialog of the symbiote Santa as he sings darker versions of Christmas carols. He also has "paindeer" that vomit symbiote goo. The best panel in the book is when Knullified Santa starts swearing. Now usually in comic books, it's blocked out by using special random characters like *&%!% but instead Santa uses christmas emojis
Marvel's armored icons team up to take down the dark version of Santa, Tony with his new armor's powers and for good measure Doom tosses in an anti-Krampus spell. Doom also fries the paindeer who had earlier spewed some of the symbiote goo on him, to no effect.
Knullifed Santa is defeated but we are left in doubt as to who he really is...could he have really be Santa or a guy from New Jersey who owns of a holiday decorations store. Doom seems to think so anyway. The only thing that I found disappointing is that there is no mention of Doom's previous encounter with Santa Claus in "I'll Be Doom for Christmas" story in What The #10 - Christmas Special from the 1980s comic.
I always have found the relationship between Tony and Victor interesting. There's isn't that deep animosity as there is with Victor and Reed. One wonders if Doom does admire Tony in some ways since he did take on the Iron Man mantle in Bendis's Infamous Iron Man series. They actually do have conversations in ways that never happen with Reed...and sometimes I don't think Tony is all that fond of Reed.