GW2 has a number of Festivals held throughout the year. This section will be updated with guides and information on each one. I recommend using tekkit's taco marker pack, as it makes completing adventures and collections much easier. More info is provided in my addons section.
Here's GuildJen's achievement guide.
Complete 5 sets of Dragon Bash dailies to get a Dragon Bash Victory Coffer, which contains a level 80 exotic weapon of your choice. The stats aren't the greatest but at least you'll get a cool skin.
With some practice, the roller beetle time trial (there's a roller beetle rental for 10 silver near it) and the pinata bashing adventure are both doing every day. This is especially true if you can get gold on both, as you'll get coffers that you can sell on the trading post for some extra gold. For the pinata bashing, I recommend using BlishHUD and Reactif markers to show you the route.
Release page. Remember to speak to Tixx every day to get a free gift :)
Star of Gratitude : This is the only time you can get this item. It eats up all those extra empyreal fragments you have clogging up your inventory/bank. Follow these instructions in order to receive the item. First, complete Grawnk Munch and then For the Children!
Secret Lair of the Snowmen - This is a strike mission, which is essentially an easier introduction to raid encounters. It should be doable by most pick-up groups but is more fun if you have a group of friends or guildies to run it with. Here’s a video guide by Kyosika on the encounter.
Winter Wonderland - This jumping puzzle is well-known for giving out a lot of wintersday gifts. It has three difficulties (left is hardest, right is easiest) and you get more gifts for doing the hardest path. To be honest, it’s not that difficult and you should aim to complete the hard path every time if you can. Here is Dulfy’s video on completing all three paths.
Bell Choir Ensemble - A fun rhythm game with multiple songs/difficulties. If you enjoy playing it and want to play music outside of this activity, look into obtaining a musical instrument.
Snowball Mayhem - PvP activity that is similar to capture the flag.
Toypocalypse - Tower defense style of game where you need to defend dolyaks against waves of enemies. You really only need walls during the phase wave or so. Invest the rest of your resources on building snowmen/catapults/ballistas and make sure to upgrade them. Two players can use rifles, two can use the candy canes and one player can use the repair pistol for CC. The pistol player should swap to rifle when Toxx arrives, as having two candy canes should be enough CC to break Toxx’s defiance bar to stun it.
Achievement guide at GuildJen - Will be updated for 2021 using a different link. Make sure to complete your Annual Achievements!
Farming Karma - If you use gw2taco, tekkit has markers showing you where the orphans are or reference this handy image guide by u/Spirean. You’ll need to buy wrapping paper and use different items (shown by vendor) to get wrapped gifts. If you’d like to buy from the TP, this link also shows what is cheapest to purchase.
Diminishing returns for Wintersday gifts purchasable by karma after buying 70 Wintersday gifts or so (breakeven might be lower this year but not sure).
Will update this section as needed, but Wintersday is fairly straight-forward.
Achievement Guide (Courtesy of GuildJen)
I'll be covering this event from the perspective of a new player. You'll receive an Invitation in the Mail that will help you teleport to and from the Hub for the event.
Section 1 - Armor
This event allows new players to obtain a full set of account-bound stat-selectable gear through a set of achievements.
1) A Royal Tradition (For Lunatic Hat) - This one is very simple. Every 2 hours, starting at 0:00 Server Time (Daily Reset), Mad King Thorn will start a game in which you must copy his emote (For example, /dance), but ONLY if he starts off by saying, "Your Mad King Says...". You'll get a point for reacting correctly. If he doesn't say "Your Mad King Says...", make sure not to do anything. Every 4 points, you'll receive a key fragment. Combine three fragments to create a key, which unlocks the chest located in The Grand Piazza of Lion's Arch. You may earn up to three key fragments per day.
2) Ascent to Madness (For Lunatic Coat) - Enter the Ascent to Madness dungeon from a gate (should be one by the Grand Piazza of Lion's Arch). Even though it was originally balanced for five players, it is possible to solo this dungeon. It'll certainly go by faster with help so either ask in Lion's Arch map chat or your guild or check the LFG Tool (Default key is "Y").
3) Lunatic Racer (For Lunatic Pants)- The race is within the Mad King's Labyrinth, which you may access through the Halloween "lobby" (use your invitation or enter a door in a capital city/Lion's Arch). I recommend finding a populated map so you'll have an easier time completing the race without being knocked off your mount. To do so, open your LFG Tool (Default key is "Y") and check under Central Tyria - Squads or Festival - Large Squads to see if there are people doing lab farms. Once you join one, you should be able to right-click the commander in your squad UI and join their instance of the Labyrinth map. There's a NPC within that should provide raptor rentals should you not have any mounts. After completing the race, you have to wait until the timer is up before leaving the map (race lasts for 8 minutes). This one is easy to complete if you're going to farming in the labyrinth anyway.
4) Mad King's Clock Tower (For Lunatic Boots) - Again, you may access this through any Halloween event gate/door. This is a timed jumping puzzle that takes new players some time to clear. It'll help to watch a video - here's one.
5) Masters of the Labyrinth (For Lunatic Shoulders) - Three bosses are located within the Mad King's Labyrinth. When looking in the LFG Tool for a lab squad, you'll notice that some commanders will be skipping the bosses so keep that in mind. You'll need to slay the Viscount, the Lich, and the Labyrinthine Horror aka Steve
6) Something Good to Eat (For Lunatic Gloves) - Open 50 Trick or Treat bags. It's really that simple. Personalized bags count, so I would just open those in case you want to sell regular Trick or Treat bags for gold.
It's likely that the Ghostly Racing Scarf (Shoulder armor) will return. Entering the Mad King's Raceway gives you access to a number of races/time trials. To earn the Scarf, you must get gold on the Roller Beetle race. The course might have changed compared to last year's so you'll have to practice it on your own. If the course is the same as last year's, it will be difficult if you're not familiar with how to drift with the roller beetle, but it's totally possible even without any special masteries. Mount rentals are free in this area. For the roller beetle race, I recommend turning on the action camera (set a key to toggle it on/off). Also look in general options -> Mounts (at the bottom) and on "Disable Conditional Mount Movement Ability Input). Mount ability 2 in your key bindings allows you to drift.
There will be a new cape that you will receive once you complete the Halloween Rituals (Annual) Achievement. Please review GuildJen's guide if you require additional information.
If you would like additional lunatic armor sets, they are craftable! You must first purchase the recipes from this vendor. These recipes are only available during Halloween. I highly recommend this for new players if you can afford purchasing them, as you can easily gear up alts in exotic armor with rare/more expensive stats (Viper's, Harrier's, Diviner's, etc) by crafting these sets.
Section 2 - Weapons and other collections
If you complete five sets of three Halloween dailies, you'll receive a box that contains a stat-selectable haunted weapon of your choice. It'll be account bound so you may move it between characters.
There are a set of collections to obtain a bunch of cool-looking back items. It starts with Mad Mysteries. Scroll down to the bottom of that page to see the following parts of the collection.
There are two weapon collections for a greatsword and shield.
Section 3 - Lab Farming
The lab gives you easy access to leveling alts and making a decent amount of gold. Don't forget to pop all relevant boosters to maximize your xp boost or magic find. Use the following guides: Looting the Labyrinth and Metabattle's Lab Farming Guide
Section 4 - Misc
https://www.thatshaman.com/tools/incursions/ <- For killing awakened for your annual/daily achievements.
Here's GuildJen's achievement guide.
If you're a new player, the Festival is split into two locations: Crown Pavilion waypoint code: [&BCwDAAA=] and Labyrinthine Cliffs waypoint code: [&BBwHAAA=]
Using the Festival Invitation you receive in the mail will take you to Labyrinthine Cliffs. That area contains a number of activities, including races, scavenger hunts, and other mini-games. You have access to vendors who will rent out mounts to you. Note that if you're a new player, you will lack the masteries to take full advantage of these mounts, but it allows you to participate in most of the activities without issue and is a great way to preview the basic functionality of each mount.
The Crown Pavilion centers around two primary activities: Boss Blitz and the Queen's Gauntlet. Boss Blitz is on the lower level and you'll most likely want to use your LFG tool to find a squad under Festivals - Large Squads (default is the "Y" key, entering the 2nd tab). You get rewards based on how quickly all six bosses are defeated. As each individual boss dies, they pass on one of their signature abilities to the bosses that are still alive. In most cases, you'll want to kill the bosses around the same time so a squad commander will call to "burn" aka kill the bosses once all of them are around 10%.
The Queen's Gauntlet may be accessed by heading towards the outside edge of the Pavilion and walking up ramps that lead to the upper level. You'll be able to fight in a bunch of solo boss encounters with optional gambits, which essentially make a fight more difficult. Please consult the achievement guide/wiki for more information and for strategies on how to defeat each boss.