A general term for Video Game features that depend on the actual date or time the game is played. For non-online games, these are usually stored as Easter Eggs. Holiday Mode may do anything from changing a single sound or sprite, to adding extra enemies, or even giving access to levels that are not normally available.
One of the most common holidays to be noted by games—especially western games—is Christmas, but other special dates or times may be observed as well.
Example triggering times:
Birthdays of the game developers
Most examples of Holiday Mode only cause very minor changes that don't alter gameplay, although some cause enough changes that they're no longer just interesting, but the whole game seems very different.
Christmas - A Santa hat for Cassat, plus all the level music in the game is replaced with a catchy tune called "Deadly Gentlemen". Considering that ROTT is a First-Person Shooter, this may make it an Anti Christmas Carol.
You can also see a picture with all the holiday hats if you wait long enough at the The End screen.
This has been expanded every year, with recent Winter Events having an entire Ski Chalet appear in Pocket D, with special missions to save Baby New Year and ski slopes with badges for fast times.
City of Heroes also features Halloween Mode which turns off the sun, allows for some very violent trick or treating, and is heralded by frequent invasions of Zombies, Vampires, Ghosts, Demons, Werewolves, Monsters and... Angry Women... for some reason.... Of lesser note is Valentines Day mode, which basically enables some extra missions in the Pocket D.
Perfect World had an amazingly annoying set of quests involving snowmen and Christmas cards in 2008.
Champions Online has a few holiday events. The most prominent is Bloodmoon which was originally for Halloween, but now happens every full moon. There's also a Christmas event, called Attack of the Misfit Toys, an April Fools Day event and an event for the anniversary of the game's release.
MapleStory has holiday-specific events, including an entire Christmas-themed distant land. During the anniversary, it had special cake monsters that (every once in a blue moon) dropped special items.
Florensia celebrated Christmas 2008 with trees and decorations in the towns, and a special Christmas soundtrack. At Thanksgiving they offered cranberry sauce as a buff item.
World of Warcraft has several themed holidays, which usually deck out the major cities in decorations and add some limited time loot and quests.
Rappelz has had candy cane monster drops and craftable Santa costumes. There is also a Christmas Rangifer, a red-nosed deerlike animal, wandering the maps. You can't attack or fight it, but if you look around nearby you may find wrapped gifts on the ground that you can gather.
In Fly FF, there have been Christmas events featuring special items and costumes. In addition, the landscape changes with respect to the seasons — red and orange trees with falling leaves in autumn, bare trees and a sprinkling of snow during the winter, and blossoms on the trees in spring.
In Guild Wars, ChristmasWintersday and Halloween were both celebrated, with certain towns being decorated for the occasion.
The Far East continent of Cantha also celebrates the lunar new year in February and the Dragon Festival which roughly corresponds to the 4th of July.
It also celebrates Talk Like A Pirate Day with a few piratey NPCs and grog as a random drop; Thanksgiving, St. Patrick's Day, and Easter with themed drops; and April Fool's Day with goofy quests and joke changes to character models.
Ace Online features several holiday events with associated changes:
Thanksgiving: Monsters drop Buff-inducing Turkeys at random.
Christmas: Snow in Arlington/Bygeniou City, Crazy Snowmen spawn, which drop Gift Boxes, Pretty Bows, and Wrappers, which can be combined at the Factory to make Presents.
Valentine's Day: Monsters drop Shield-restoring Chocolates.
For Valentine's this 2009, Bloody Valentines event is in effect - As of the latest patch, Event Mobs spawn in New Bark City and the Pandea Maps that may dropBroken Hearts. These Broken Hearts may be combined into even-exclusive marks or event-exclusive capsules.
For 2009 New Year's Event, Special Event bosses will spawn in mid-to-high level areas. They have a chance of dropping rare event items that can be combined into equippable holographic Marks.
Star Wars: Galaxies got into the act too. The Star Wars Holiday Special, as much as everyone would rather forget it, had already given them Wookiee Life Day for Christmas... and as luck would have it, the Republic was founded on July 4th. And you celebrate it with fireworks and parades. How fortunate!
Not to mention the Ewok Love Festival!
Billy Vs SNAKEMAN has some kind of Holiday Mode content active during half the year, mostly in the form of quests, but some months add items to what you can find while Collecting Ingredients or buy from the NPC vendor. Also, the village upgrade 'Ninja-Mas Tree' only does anything in December (And does it's thing ten times as well on the 25th).
Kingdom of Loathing acknowledges most real-world holidays, sometimes in altered form (e.g. Easter becomes Oyster Egg Day).
These are recognized both on their real-life dates, and the corresponding dates to the in-game calendar to the first day each one was celebrated. A notable exception is Christmas, which has two in-game holidays: Yuletide is a day-long celebration occurring every Dougtember, while Crimbo is a month-long celebration, which takes place every December.
In 2006, KoL-calendar Halloween fell on real-world December 25th. Result: a The Nightmare Before Christmas-inspired "Crimboween" celebrated on October 31st.
For the first few years of the game, the Thanksgiving analogue "Feast of Boris" wasn't celebrated on real-world Thanksgiving because the possibility that real-world Thanksgiving would fall on a stat day would lead to absolutely broken speedruns that couldn't be challenged until the next time such an occurrence happened. This eventually did happen.
zOMG! celebrates quite a few major holidays, including Halloween, Christmas, Easter, and April Fool's Day. All of these events give you limited-edition loot and/or items for your avatar.
Backpedaling a bit, zOMG!'s parent site Gaia Online goes into Holiday Mode for most major events, but especially for Halloween and Christmas. Halloween and Christmas feature header changes, NPC Costumes, special events (and on Halloween, the introduction of a new Race) zOMG events, and a reskin for Gaia Towns. (The normally decorative fountain becomes a Swimming Pool, Graveyard, or frozen pond depending on the time of year.) Gaians love to join in the fun, frequently going into Holiday Mode themselves.
Final Fantasy XI celebrates a number of Japanese-specific and worldwide holidays, although usually given Vana'diel-specific names and customs. The Harvest Festival happens around Halloween, for example, and still involves costumes as various monsters, Jack-o-lanterns, and handing out candy.
Specifically, there is New Year's, Valentione's Day (Valentine's Day), Doll Festival and Feast of Swords (both related to Children's Day in Japan), Egg-stravaganza (Easter), Harvest Festival (Halloween), and the Starlight Festival (Christmas). There's also Celestial Nights and the Sunbreeze Festival during the summer,they don't appear to be related to specific holidays. Both Sunbreeze Festival and Starlight Festival have unique music playing at times in the towns, and there are fireworks during the former.
Earth Eternal had an event called "Winter Dawning" that was decorated with Christmas themes, and it lasted for a month.
Runescape celebrates Christmas, Easter, Thanksgiving, and Halloween with somewhat large events which tend to involve short quest type things, giving out unique, untradeable rewards that are only available during their respective holiday seasons that year. Each holiday has begun to develop its own storyline. Originally, holidays were celebrated with massive, one-day holiday drops of tradeable holiday items which now sell for prices disproportionate to their utility. The Santa hats dropped in 2002 are now rare enough to sell for millions of coins, and a collection of the five, different colored party hats of 2001 now costs over 2 billion coins, which is MORE COINS THAN IT IS POSSIBLE TO HAVE AT ANY POINT IN THE GAME. The impact of these prices on the game's economy is the reason that holiday items released now are untradeable.
Tyrian prompts you if you want to play with Holiday Mode on when you start the game during the month of December or through the YESXMAS command-line parameter. Many sprite graphics are replaced and instead of a computer voice saying "Good Luck" at the start of a level, a different voice says "Merry Christmas".
Raptor: Call of the Shadows has a birthday mode. Certain dates, which are the birthdays of some of the developers, give a non-standard version of the Apogee theme sung by said developpers and automatically activate the game's Silliness Switch cheat, which is anything but silly in difficulty as it adds lots of extra, very tough, enemies to the levels. These extra enemies are so tough it takes several shots from the most powerful weapon in the game to destroy them.
Team Fortress had a party mode which could be activated by the server operator and gave all the characters party hats, changed grenades into gifts, and altered all the death announcements to fit the theme. Team Fortress 2 does the same thing, but sets it to automatically kick on to celebrate the week that the original game was released.
There's also a Halloween mode (that began in 2009), where taunts are often replaced with a dance move from the music video for Michael Jackson's Thriller.
December has Australian Christmas (or Smissmas), where crates drop containing valuable loot that can be opened with specialized keys. In 2010 there was one variety that contained hats and miscs, where in 2011 they were separated into Naughty and Nice crates, the latter containing Christmas lights to decorate stock weapons with and the latter containing new aesthetic items. In 2012 and 2013, the Naughty and Nice crates returned, this time the Naughty crates giving pre-decorated festive versions of several weapons.
Online third-person shooter GunZ: The Duel has a Christmas version of its popular town level that shows up only around Christmas time. After Christmas is over, the level is gone.
Call of Duty: Modern Warfare has the level "Winter Crash", which is a Christmas-themed version of the level "Crash", complete with lots of snow, lights, and even the occasional sound of Santa in the distance.
Animal Crossing famously celebrates holidays. The Japanese version would have events themed after holidays such as Golden Week, while the localized American version celebrated Labor Day and other U.S. holidays. Internationally known holidays like Christmas and Halloween were celebrated in all versions. The later games, however, celebrated made-up holidays instead, to make localization easier. City Folk and New Leaf bring back regional holidays, and keeps them enabled during Wi-Fi play, encouraging people to visit international friends to participate in their holidays.
Also, you are given a piece of birthday cake on your birthday by a random villager, which increases your feng shui, and you might also get birthday cards with gifts in the mail.
In New Leaf, talking to K.K. Slider on the Saturday before your birthday (or the day of if your birthday falls on a Saturday) leads to him playing a special birthday song for you, only obtainable this way.
In Lexi-Cross, host Chip Ramsey had special pre-game messages for certain U.S. holidays.
In the independent fan-game Sonic Robo Blast 2, the game adds hidden Easter eggs to collect around Easter time, and even keeps track permanently of which ones you collected (so if you don't get them all during one Easter time, you can finish the job the next year). During Christmas time, the game does a total visual and aural overhaul. The music for every level is replaced with a different Christmas tune, snow falls in every level, and many textures change.
The city in Shenmue gets redecorated for Christmas and other holidays, most of which the player will never see since it's easy to complete the game before then.
Christmas Nights was a one level demo of NiGHTS Into Dreams for the Sega Saturn, whose main feature not present in the original game was to change the graphics and models based on the time of year. One of the fan favourites was on April Fool's Day, where Reala's character model would replace that of NiGHTS!
And on the Updated Re-release on the PlayStation 2, the Christmas NiGHTS mode also exists.
Really, most games that feature NiGHTS (even as a cameo) have some special event on both Christmas and April Fools Day. For example in Sonic Shuffle, Lumina's model would be replaced with NiGHTS' on Christmas and Reala's on April 1st. In Journey of Dreams, the My Dream room's music would change on these holidays.
While on the topic of Journey of Dreams, the game was even announced on April 1st and released Christmas season of the same year.
Around Christmas time, Sonic Adventure allowed players to download a patch which added a Christmas tree to Station Square. Its sequel featured unlockable costumes for both Halloween and Christmas.
The multimedia player/streamer/recorder VLC Media Player has a traffic cone as its tray icon. Around Christmas time, the traffic cone will be seen wearing a Santa hat.
In Crusader, starting the game on Christmas will result in a special bonus level where you're surrounded by a dozen of the end boss in an open room with no cover, while you're armed with every gun in the game, and a techno-industrial remix of Christmas carols plays.
In Metal Gear Solid 2, the Gurlukovich soldiers carry dog tags bearing the personal information of Metal Gear fans who sent in their details. If you steal a soldier's dog tag, and examine them through the Scope/Camera with the Triangle button, and the date corresponds to the date of birth of the soldier, you'll see the words 'HAPPY BIRTHDAY' pop up on screen. A similar thing happens if, when putting your name in the Node at the beginning, you put in that day's date as your date of birth.
The Simpsons Hit & Run had a festive version of the main menu, as well as a creepy version for Halloween and a romantic version for Valentine's Day.
An old update of Fraxy had a secret mode on April 1st; a secret mode based off of Gradius, complete with autoscrolling and an inability to turn (and turned the player into the Vic freaking Viper!). Later updates added the Vic Viper, the option to turn on autoscrolling, and a scenario mode based on the one that came with the Holiday Mode.
Dungeon Keeper had a secret level that was only accessible during a full moon. The game also showed happy birthday messages for the developers when it started.
Operation Flashpoint of all games did this. Around Christmas time all of the small pine trees turn into Christmas trees, complete with presents.
Partial example: NetHack subtly changes the game mechanics based on time of day and moon phase. For example, dogs are harder to tame at night during a full moon, and some monsters give different messages when talked to at night. A somewhat straighter example is a minor luck penalty on Friday the 13th.
The Simpsons Road Rage has several characters who are only available on certain days of the year - Christmas Apu on December 25th, Hallowe'en Bart on October 31st, Thanksgiving Marge on the fourth Sunday in November, and New Year Krusty on January 1st.
In Zoo Tycoon you can purchase a Jack Lantern on Halloween, and a Snowman on Christmas (game time). The days in Zoo Tycoon last a few seconds, but you can place all the special ornaments you like if you pause the game in those specific days. Also, Santa's sleigh, a witch on a broomstick, and a biplane with a Blue Fang sign will fly over on appropriate days. (The last one marks the signing of an agreement with Microsoft or something.)
Civilization III had a (mass) regicide mode, with (a) king unit(s) that had to be killed to win. If the computer clock's is set to January 8 (Presley's birthday), the king unit is ... well, The King.
Ancient Domains of Mystery has special effects for Mondays, Friday the 13th, Christmas, New Year, and the game creator Thomas Biskup's birthday (July 2nd).
Non-game example: the free text editor EditPad produces special messages in the status bar on Christmas, New Year, and the programmer's birthday (February 16th).
the second and third Ratchet & Clank games have a Developer's Room called the "Insomniac Museum" that is usually available only after getting 100% Completion. True to its name however (in spite of being named after the developers of the game), the teleporter to the Museum will freely activate between the hours of 2AM and 3AM.
In Sid Meier’s Pirates!, if your computer clock is set to September 19th (International Talk Like a Pirate Day), all the dialogue in the game is piratized.
In most of the You Don't Know Jack games, the voice that greets you as you start the game would have something special to say on holidays and various other occasions, including Elvis' birthday, the anniversary of the game's release, or if you were playing especially late at night. If you played a one player game on a weekend evening, it would criticize your lack of social life.
Turn on a Nintendo DS on your birthday (which you can input into its memory) and you get a special activation jingle, as well as a birthday notification in PictoChat. Sadly, the DSi does not do this.
Mega Man ZX: Advent had unique chips and items that could be attained in one of two rooms depending on the month.
Pokémon Diamond, Pearl, and Platinum do this as well. Only you don't get anything out of it. On your birthday, by talking to Lucas or Dawn (depending on who you're playing as), they'll acknowledge the fact that it's your birthday and congratulate you.
Pokémon - XY has the first Pokemon Center greet you with a surprise party and a birthday cake on the screen above the front desk. It also switches the music to a music box version of the Pokemon Center theme and Nurse Joy greets you with a Happy Birthday.
Kirby Squeak Squad did it too, with a special graphic with most of the characters and a giant cake that appeared before entering the menu. All it said was 'happy birthday.'
The DS The Legendary Starfy game does basically the same thing. You turn on the game, and you get a cute "Happy Birthday" graphic with a cake before you go to the start menu.
Trainers in Sinnoh in Pokémon Diamond and Pearl can enjoy Diamond Dust weather instead of snow at Snowpoint City on several notable days, including certain holidays and developer Junichi Masuda's birthday on January 12.
Tsukihime has a small sketch if you play it around Christmas time involving some of the odder characters available.
Its spin-off, Melty Blood, did this, too: the title screen features different artwork depending on when you play it, including Christmas Eve and Ren's birthday.
One Halo 3 multiplayer map, Valhalla, has a large wall on one side that features a different image on certain days of the year, including Veteran's Day, Halloween, and July 7 (Bungie Day).
Halo 3 also displays joke "advice" messages on April Fool's Day. One was something to the effect of, "You can avoid damage from a grenade if you sit on it like a goose."
The December 25 Christmas tree in Dark Castle's Great Hall was one of the most beloved easter eggs on early Macintoshes.
Start up SimCity 4 on December 25 and load a city. If there is an area of the city with sufficient elevation, snow will appear on those areas when it's wintertime.
Motor Mayhem puts Santa hats on all of the characters if you play the game on Christmas.
Recent versions of the Lasertron laser tag system allow the operator to mark certain players as having a birthday. If any players are so marked, the computerized announcer will say "Now activating birthday players!" and that player's vest will actually wish them a happy birthday at the end of each game.
In Art of Fighting 3, each character has a birthday. If the game is played on a certain character's birthday, that character will become stronger and have the ability to perform their Desperation Attack at any time (which normally only happens when they are low on health).
In LittleBigPlanet, holiday downloadable content is released and sometimes free. This includes Leprechaun, Santa, and other costumes, along with some packs.
In Donkey Kong Country 3, inputting a code in the file select screen could changes the bonus rooms music's and bonus item look to a Christmas theme.
The Wiiware version of Cave Story replaces the protagonists' sprites on Halloween and Christmas. On Halloween, he's a zombie and he receives a pumpkin mask in the Plantation; on Christmas, he's dressed like Santa and receives a reindeer mask.
In Cave Story+, most of the sprites are changed for Christmas.
Most? Nearly all the sprites are changed for Christmas; the player sprites, the NPC sprites, the bosses, the enemies, the item drops. Experience drops are changed to jingle bells, the missile drops have little ribbons tied around them, and the Demon Crown becomes a boxed present the Doctor wears on his head. And the Halloween sprites are just as elaborate◊.
The greeting in Stronghold is changed to "Merry Christmas, my Lord!" if you play on the 25th.
On April 1, in Black & White, the Creature's footprints will be replaced by smiley faces.
Scooby-Doo: Night of a Hundred Frights has hearts on all the Scooby Snacks on February 14, snow everywhere on December 25, and fireworks in the background on December 31.
Monster Rancher DS combines this with Video Game Time. On the in-game week that would correspond with your system-entered birthday, either your assistant, your monster, or your pet owl will give you a gift.
DEFCON of all games, has a Christmas modification: the whole world is seen from a polar perspective, reindeer fly instead of bombers, the haunting soundtrack is replaced by Christmas songs, and instead of the "5 million dead" it's "5 million children made happy". That's right, you're playing as multiple factions of Santa, all struggling to deliver presents. It adds a surreal sense of heartwarming to a cutthroat game of nuclear war.
Playing LEGO Loco during Easter, Halloween, and Christmas unlocks special holiday pieces, as well as seasonal pieces.
And Google's, which vary from holidays such as Christmas to the birth date of various famous people.
In universe example: Your Pip Boy in Fallout 2 would wish you a merry Christmas if the in game date was December 25th.
When logging into Microsoft Bob on your birthday, your animated host will wish you happy birthday, complete with a cake, balloons and confetti appearing in the room.
The (unnamed) MMO played by The Guild had one such holiday as a plot point, where a real life gathering was planned to celebrate the end of the in-game festival season.
After beating D2 and sitting through the end credits, a clock appears counting down to (or the time past) December 31, 1999. If the player alters the Dreamcast's internal clock so that this post-credits display reaches midnight on New Year's Day, it triggers the message "Welcome to the 21st Century!"
Not only that, but if you try to play a Dreamcast demo disc from the official magazine around Christmas the background will be Christmas themed.
In the Munchers series of edutainment computer games (i.e., Number Munchers, Word Munchers), between December 1 and Christmas, one of the titular Munchers wears a Santa hat. However, this only occurs with computers that can remember the time/date or by leaving on a computer constantly, since not all computers were capable of such technology at the time.
In Batman: Arkham City, going to see Calendar Man on certain holidays will result in him telling you a story about a crime he committed on that day. On Mother's Day and Father's Day when he tells you how he killed his mother and father on those days. Never said Holiday Mode had to have cheery events! Doing this for all the holidays is required for the "Storyteller" achievement.
In Dragon Quest IX, you can get holiday-themed items such as a cake if you use DLC at Christmas.
Enemies in Killing Floor get reskinned during the Christmas, Halloween and summer periods. (If you want to know, the summer theme is "circus freaks". The Halloween mode was also changed in 2012 from generic Halloween monsters to Hillbilly Horror)
Gears of War 3 unlocks special holiday events in multiplayer: Pumpkin heads for Halloween, Exploding turkey / chicken launchers for Thanksgiving, Snowman heads for Christmas, and a Locust in football pads for Super Bowl week.
Planetside has holiday specific events. On Christmas, snowmen and gingerbread men are placed on a variety of the maps (include the deserts), and finding them grants you use of a special item for the duration of the event. Other holidays, such as Halloween, have different events each year.
Madden NFL will appropriately mark up the field for October (breast cancer awareness month), as well as holidays. The game will also attempt to match the current weather at the stadium where you are playing, due to a partnership with the Weather Channel.
Fable Heroes has the players all gain pumpkin heads if they play on Halloween.
Minecraft for Halloween 2012 had zombies, skeletons, and zombie pigmen occasionally spawn in the game with a pumpkin or a jack o' lantern for a head instead of their regular heads.
Another update for Christmas 2012 changed the skins on Chests to make them look like wrapped gift boxes.
Terraria first had one for 1.1.1 when the game is played from December 15th to 31st which always caused a snow biome to generate when creating a new world instead of a 1/3 chance the rest of the year (this was changed in 1.2 when the snow and ice biome was made more significant). Enemies would occasionally drop presents that contained red/green candy cane blocks for building and would contain a snowglobe if the world was in hardmode. If used, it would summon the Frost Legion that when defeated, allowed Santa Claus to move in which he could sell you Santa's clothes and decorative Christmas lights.
1.2.1 introduced the Halloween event for October. Pumpkins grew throughout the world during this time (and they could be grown outside of the event using pumpkin seeds from the dryad). Enemies occasionally dropped goodie bags that contained various costumes, paintings, rotten eggs and even a pet item. Enemies can be seen wearing various costumes. The heart and mana pickups were even replaced by candy apples and soul cakes, respectively. Finally, there is the pumpkin moon event that took place in waves and had you fight two minibosses (the Mourning Wood and Pumpking) that would drop special items the more waves you were into the event.
PAYDAY: The Heist had gift boxes very well hidden during the Christmas season in 2011 and 2012. Players who found the boxes unlocked the Santa mask and an achievement.
Around Halloween, Haven gets darker and pumpkins are scattered around. You get to hunt for the Punkin King, who gives you three types of candy. Each of these candies is exchanged for a different type of mask, the higher-priced versions of which look less like a cheap cardboard mask and the most expensive versions lasting permanently. Each candy can also be traded for boxes which give you orange versions of lower-tier armor.
Around the Holiday season, Haven is covered with snow and festive decorations and the characters celebrate Winterfest. You get to help out Impostoclaus (a giant jelly with a moustache, glasses, a pipe, and a santa hat) who gives you tokens that you can trade in for Santy hats, the more expensive versions of which cause snow to fall around you. The tokens can also be traded in for boxes which give you white versions of lower-tier armor.
Lastly, around the time when Spiral Knights was released, you get to help out a baker whose cakes turned into monsters. Haven doesn't actually change much for this event, but you can trade in the tokens from the monster-cakes for cupcake-esque hats, the most expensive version of which matches your player's color and lasts permanently.
BIT.TRIP RUNNER automatically changes to a Christmas theme in December. Commander Video's cape changes to a red and white pattern, and he wears a Santa Hat on the main menu. The main menu music is also replaced with chiptune Christmas music.
The Mario fan game Super Mario Blue Twilight DX has this for Christmas, April Fool's Day and (obviously) Halloween. To note:
On Halloween, the true final level is unlocked and you get to face Dracula in a true final battle for the real ending.
On Christmas, you unlock a mini 'side game' of sorts, showing Mario's quest to save Christmas by finding the ornaments stolen from the Mushroom Kingdom Christmas Tree. Cue two new levels with new enemies, graphics and music.
On April Fool's Day, Mario gets to visit Green Hill Zone and fight Sonic the Hedgehog. Actually Metal Sonic
And unlike in many fan games, these bonuses genuinely are tied to the computer's sytem clock. Which has probably confused a few people given that the final level and good ending is only legitimately playable in one day of the entire year.
In The Denpa Men, if you talk to your Denpa Men on Christmas, they'll acknowledge it. In addition to wishing you Merry Christmas, they'll also make observations, such as wondering why Santa hasn't been busted for breaking and entering yet.