In Dragon Ball Z, the battle against Freeza occurred on Christmas. Unlike other examples, this one is likely a mere coincidence, as this isn't pointed out in-series, but it's All There in the Manual.
In GT, the final battle against Baby is on the day before Christmas too.
The Karas OVA take place entirely around Christmas-time, when much of the city's population gets eaten/drained of all their blood by evil robotic demons, which also destroy most of the city.
Macross had Giant Alien Terrorist Santa activating bombs after a raid on Christmas Eve. Followed by the survivors singing Silent Night.
Although it's not heavily focused on, the climatic final battle in the manga version Chrono Crusade takes place from Christmas Eve to the dawn of Christmas. At one point, Chrono mentions to Rosette that it means they'll have something new to celebrate every year if they're victorious.
The anime of Asobi ni Iku yo! has the last three episodes take place at Christmas. The Catian mothership is attacked and taken over by Dogisian forces, and its orbit is set to decay and crash into Earth, forcing the humans to blow the ship up if the main characters can't stop it in time. They do, and the Catians give humanity a 'Christmas gift' in the form of a space elevator that looks like a giant Christmas tree.
The Sailor Moon S movie takes place around Christmas, though not explicitly on the day. Bonus points for Tuxedo Kamen dressing up as Santa Claus.
Batman goes through this all. the. friggin'. time. If there's one hero that never takes the day off during the holidays, it's Batman. His enemies LOVE to stir up crap during Christmas, especially guys like The Joker, Mister Freeze and The Calendar Man.
In the Justice League of America comic book series there was a story in the 70s called "2000 Light Years to Christmas!" In it, the League must recover three powerful objects that some aliens have lost on Earth; one of them falls in the hands of a little girl who lost her family in a Middle Eastern war, and uses it for revenge against the invaders. While there is plenty of action, in the end the girl is convinced to surrender the object peacefully by Red Tornado. It is later revealed that the objects were actually intended as gifts... for a messiah being born in another world! Oh, and Tornado, who is android, adopts the little girl as his daughter.
Marvel Comics occasionally publishes Christmas Specials focused on The Punisher, which usually feature two things; Frank dressing up as Santa, and Frank killing a lot of bad guys. Oftentimes, he does both simultaneously.
The original Teenage Mutant Ninja Turtles comic had, early in its run, four one-shot "micro-series" that focused on each individual Turtle. Both the Michaelangelo and Leonardo one-shots took place at Christmas, and featured lots of action scenes:
In the Michaelangelo one-shot, Mike went out on Christmas Eve to enjoy the Christmas sights, play in the snow, shop for Christmas presents, adopt a homeless cat... and get involved in a high-speed car chase with gun-packing robbers. The comic was eventually adapted into the episode The Christmas Aliens in the third season of the second animated series.
The Leonardo one-shot is pretty much one long action scene, featuring Leonardo fighting an impossible number of Foot ninjas — interspersed with small snippets of the three other Turtles, together with April and Splinter (and Klunk the cat) making Christmas preparations. Like the Michaelangelo special, it was adapted into an episode of the second animated series, but without the Christmas elements.
In issue #13 of Paperinik New Adventures "The Darkest Night",Paperinik had to fight the Evronians on Christmas's Eve to rescue the people of a small village near Duckburg.
In one side story of the Alternian Nation Series, Karkat and Gamzee's first experience with Christmas involved hiding inside a mall during a storm, being discovered and fed by a security guard, and having to later drive off some thugs who had broken in and were attacking him.
A Growing Affection: Naruto and Hinata's first Yuletide together involves saving Santa from ninja puppeteers who want him to repair and upgrade their puppets.
Batman Returns. The main story begins with the Red Triangle Circus crashing Gotham's tree-lighting ceremony, complete with clowns with Uzis, a Gatling gun mounted on a barrel organ, a fire breather setting a toy store ablaze, and the strongman beating down a Salvation Army Santa with his own sled.
Spoofed at the beginning of Scrooged, with a fake trailer for The Night The Reindeer Died.
The Stallone movie Cobra takes place during the Christmas season, although it's not hugely emphasized.
Behind Enemy Lines: Burnett's troubles begin when Admiral Reigart puts him on a reconnaissance mission, forcing him to miss the Christmas celebration on the ship.
The first three Home Alone movies. Kid defeats gang of thieves by turning his house into a Death Course. In the first two movies, it helped set the scene for the conflict between Kevin and his family. In the third... it was just because.
It did provide a convenient plot device to get the McGuffin into the kid's hands in the third movie.
Iron Man 3 takes place in the lead-up to Christmas.
The French Connection doesn't make a big deal out of it, but little holiday elements like Popeye undercover dressed as Santa Claus, different store windows loaded with Christmas decorations and the bitter winter cold continually pop up.
In Getaway, Brent and his wife Leanne went to her hometown of Sofia, Bulgaria for a Christmas vacation, only for her to be kidnapped and him forced to drive around performing the kidnapper's orders to get her back.
In L. Frank Baum's The Life & Adventures of Santa Claus, Santa's toys are stolen by creatures who want kids to receive them through evil deeds rather than good. This pisses off the Great Ak and the forest immortals, Santa's chief supporters, and a war between mythical races ensues.
"Santa Claus vs. S.P.I.D.E.R." by Harlan Ellison. When he's not wearing the red suit, Kris looks and acts something like James Bond. And the red suit's got body armor, rockets in the boots to jump long distances, machine guns and high-pressure flamethrowers up the sleeves.... "Ho ho ho."
Legacies is a Repairman Jack novel set shortly before Christmas; one early incident features Jack dressing up as Santa to beat the living crap out of a scumbag who stole toys from a children's AIDS clinic.
Engine Sentai Go-onger sees the heroes team up with Santa using his magic sack to fight one of the main generals of the Gaiark. In Kaizoku Sentai Gokaiger, Gai goes the extra mile and merges the Red and Green Ranger Keys so he can become "Gokai Christmas".
Every time Doctor Who has a Christmas Episode, something disastrous happens. Aliens invade (the Sycorax), giant spaceships threaten to crash and destroy the Earth, weird robot Santas go around murdering people, and more alien invasions in the form of the Racnoss and her children. In fact, Christmas episodes are extra-long and twice as epic as normal episodes, second only to season finales in terms of how they'll go all-out.
Lampshaded in Voyage of the Damned - The Doctor and Astrid land on Earth at Christmas time and find the city deserted. Just when you think that's the mystery of the episode, Bernard Cribbins tells him the reason that the city is empty is that everyone has evacuated the city thinking that something awful is going to happen. (They're right.)
But, just to show you that the universe punishes people for being too Genre Savvy, evacuating London won't actually help in any way at all this time if the Doctor can't fix it.
Lampshaded again later on in the same episode:
The Doctor: Actually, that's not true. Christmas is a time of peace and thanksgiving and... What am I on about? All my Christmases are like this.
In the McGann movie, near the end, the Doctor warns Chang Lee, "Next Christmas, take a vacation. Don't be here." However, here the Doctor is referring to San Francisco, not London.
The Monk Christmas episode Mr. Monk and the Man Who Shot Santa, the end of which features Monk pursuing a jewel thief and beating him with a giant candy cane yard decoration.
A Saturday Night Live sketch from the 1980-1981 season had a fake trailer for a movie called "Kung Fu Christmas," starring Caine (David Carradine's character from the show "Kung Fu," played by Carradine himself) and Bruce Lee (played by Eddie Murphy).
An episode of Xena that takes place around Winter Solstice, with her and Gabrielle acting out Scrooge's Christmas story.
The made-for-TV movie The Crossing depicts the below-mentioned crossing of the Delaware and Battle of Trenton, including the popular but untrue notion that the efficacy of the ambush was due to the Hessians being fantastically hungover after a German Christmas.
"Peace on earth everybody and good will toward men"
And yust at that moment someone slugs Uncle Ben.
"Santa's Gonna Kick Your Ass" by The Arrogant Worms
On Mp3.com, a comedy team called Prime Example did a spoof advertisement for the ultimate Christmas TV special "Violent Night" in which Santa Claus, Rudolph, Frosty, Charlie Brown, and the Little Drummer Boy team up to save Christmas from a war on Christmas by the Grinch, Ebeneezer Scrooge, the Abominable Snowman, and Satan. Arnold Schwarzenegger plays a Terminator-esque Santa Claus with an assault rifle, and Clint Eastwood plays a Dirty Harry-esque Ebeneezer Scrooge with a shotgun... coming up next on Fox!
And Tsion Ben-Judah gets to witness it in the Left Behind book The Indwelling.
Even older than that, although not by much: the original birth of Christ in the Gospels took place against a backdrop of Roman occupation, mass infanticide, parents fleeing the country to save their baby...
The Final Battle of Dino Attack RPG took place only a few days before Christmas. This was acknowledge by several Dino Attack agents who, fearing they might not survive the battle, decided to celebrate Christmas during the battle.
Santa's Soldiers from Deep 7 Games. It's a parody of the Rankin-Bass Christmas specials where you are playing a paramilitary strike team of cute Christmas elves.
The infamous Risus adventure "Kringle All the Way," which starts with versions of Santa representing the Seven Deadly Sins setting out to assassinate Ebenezer Scrooge, Jesus, and Christmas shopping so he'll have the holiday to himself.
Snatcher takes place in the last week of December, Jingle Bells plays in the Alton Plaza area and your contact, Napoleon, appears before you dressed in a Santa outfit at one point.
Muv-Luv Alternative: When's the best time "A single child could give hope to humanity"... by deploying a massive army of mecha onto a BETA controlled island in Japan and using a giant floating weapon armed with a Charged Particle Cannon to kill thousands upon thousands of said BETA? Why that'd be Christmas Day, 2001. Of course, nothing going right ever.
Surprisingly averted in Team Fortress 2 proper; despite four straight years of Halloween maps and three annual "Australian Christmas"/"Smissmas" events that add "festive" items to the game, no official map has ever been released that takes place at Christmas. The supplementary comic "A Smissmas Story", however, fits the bill pretty well.
The second season of Sam & Max: Freelance Police features a North Pole episode that ends with a gun battle with a demonically-possessed Santa Claus. Their ancestors, Sameth and Maximus, have a run-in with a suspiciously familiar toymaker with elf minions in season three.
Sluggy Freelance had some epic confrontations between Santa Clause and Bun-Bun, culminating in the Holiday Wars where Bun-Bun attempted to take over all of the holidays. This annual event has been quiet for several years now; too quiet...
Bun-Bun is a bit...preoccupied with other things these days.
Bun-Bun: You guys run around like special-needs-kids until one of you causes Oasis to rear her pretty head. And then I pay her back so hard she'll stay dead out of sheer terror of me.
The Whateley Universe authors really like this trope. "Christmas Elves" has Fey and Generator in a fight to the death inside a Syndicate hardsite. "Ayla and the Grinch" has Phase against a serial killer. "There's an Angel in Father John's Basement" has Seraphim, "Christmas Crisis" has Tennyo, "Have Yourself an Evil Little Christmas" has the Bad Seeds, "Summoning Sweeties" has Gateway and Bladedancer, "The Case of the Poisonous Patent" has Loophole and her friends, "Have Yourself a Monkey Little Christmas" has Chaka and Bladedancer, ... And all of these take place during the same Christmas break!
The show typically has a rather surreal Christmas Episode, but Season 5's "Rapture's Delight" takes the cake, with a bizarre crossover parody of Left Behind and homage to Mad Max and Escape from New York. After the Rapture, Bad Ass Jesus recruits a grizzled, bitter, hook-handed Stan on one last mission to raid the Antichrist's lair and rescue Francine using lots of guns and explosives. It must be seen to be believed.
In season 6, Steve accidentally killed Santa, so the family buried his body in the woods. Only, Santa wasn't quite dead, and using the powers of science Santa was healed, only to swear revenge on the Smiths. This eventually lead to a bloody battle between the family and Santa and his army of elves. Although the battle was cut short because he had to leave at daybreak, he promised to return to kill them next year.
Parodied on Family Guy with Kiss Save Santa, because everyone knows "Pterodactyls hate nothing more than the screech on an electric guitar."
Transformers Animated: 'Human Error'. Soundwave reappears for the first time since season one and traps the Autobots in a Lotus-Eater Machine simulation in which they are all human, so he can turn them into Decepticons. Sari recruits a bunch of second-string characters to help free them, and it all ends in a literal example of Autobots, Rock Out!.
"And now, the Christmas Special nobody wants to see, but everyone will watch. It's Christmas with the Joker!"
There's also the second Christmas special, with three stories set over the Christmas to New Year period. The first story has Harley Quinn and Poison Ivy kidnap Bruce Wayne, the second has Batgirl, Harvey Bullock and Renee Montoya fighting Clayface in a shopping mall on Christmas Eve, and the third has Batman and Robin stopping The Joker from killing thousands of people at the New Year countdown in Gotham Square.
Zig-zagged in the Justice League Christmas episode. Clark brings Martian Manhunter to the Kent farm, Flash finds some orphans the year's most popular toy but had a fight with the Ultra-Humanite in the process, and John (Green Lantern) takes Shayera (Hawkgirl) sledding, which turns into a super-powered Snowball Fight. Shayera then shows John what she does for fun - visit alien bars and start fights. The episode ends with them (and the rest of the brawlers) passed out, sleeping peacefully.
The Venture Bros. Christmas special has Brock, dressed as Santa, in a no-holds-barred fight with the party-crasher Krampus.
In addition to the Dragon Ball Z examples above, Robot Chicken once did a Christmas sketch in which Goku and Gohan go to the North Pole to fight a half-Santa, half-snowman monster. Eventually Mrs. Clause morphs into what Tetsuo becomes at the end of AKIRA and Santa resolves never to visit Japan ever again.
Futurama: two Christmas specials with a killer robot Santa and a sack full of ammunition-related puns ("your mistletoe is no match for my T.O.E. missile"). Plus this shows up again in the animated film Bender's Big Score, including an awesome song "This Trinity's Goin' to War" when Robot Santa used his toy workshop on Neptune to manufacture weapons, with the help of Kwanzaabot and the Chanukah Zombie.
Not to mention the finale of broadcast season seven The Futurama Holiday Spectacular that has not only a Christmas storyline but also action filled Robanukah and Kwanzaa.
The He-Man and the Masters of the Universe (1983)/She-Ra: Princess of Power crossover Christmas Movie had the twins and their allies fighting to protect two Earth children from Horde Prime because of the villain's fear of their "Christmas Spirit." (To be fair, when being evil is your stock in trade you don't want people to be happy, anyway.) The day is saved, of course... by Skeletor! Apparently, Horde Prime was right to worry about the Christmas Spirit being infectious.
The episode "The Christmas Aliens" of the second Teenage Mutant Ninja Turtles animated series features Michelangelo going out on Christmas Eve to do some last-minute shopping while his family prepare for a big Christmas party, and ending up fighting against criminals who are stealing toys that were supposed to go to an orphanage. The story's an expanded version of the Michaelangelo one-shot comic from the original Mirage comic.
Defied during the first year of World War I, wherein the soldiers on both sides got out of the trenches voluntarily stopped the war, without any such orders from command, to have a real Christmas. They played football (European style) in the no mans lands between the trenches. There are also stories of decorating trees and exchanging gifts.
One group took advantage of this to capture a strategic point, to the shock of everyone.
There's also a story of a group of American and German soldiers meeting in a forest on Christmas, both seeking shelter from a snowstorm, the elderly German woman who lives there doesn't allow them to fight in any way, and it ends with them singing Christmas carols together, even though they don't understand each others language.
Hanukkah: if you don't know, this is a Jewish holiday at about the same time of the year as Christmas (and tends to absorb elements thereof by cultural osmosis) that commemorates asskicking.
The Battle of Ortona.
Averted in 1916, when German and Canadian soldiers near Vimy Ridge exchanged gifts.
During the Civil War, General Sherman captured Savannah, GA days before Christmas 1864 and presented it to President Lincoln as a Christmas present.
The Battle of Hong Kong during the Pacific War. The Japanese captures it from the British on December 25, 1941
The Battle of Wake Island
In the Sendling Christmas Massacre of 1705, almost three thousand Bavarianrebels tried to storm the city of Munich while it was occupied by Austrian troops, only to be betrayed, surrounded, forced to surrender, and massacred in the same night. Still widely known as the Sendlinger Mordweihnacht (Sendling Murder Christmas).