Currently, the fastest method of getting Candy Corns is getting large amounts of Trick-or-Treat Bags from the Mad King's Realm with a zerg. Run around the Labyrinth with a zerg and open the Haunted Doors while simultaneously mining the nearby Candy Corn Veins. Personally, I was able to get over 1000 Candy Corns in about 2 hours on the first night of the holiday while leading the zerg.
There are three types of events that start when opening doors:
- Boss event: Spawns one of the champion bosses
- Veteran event: Spawns a veteran enemy and potentially some normal enemies as reinforcements
- Normal event: Spawns a large amount of normal enemies
The normal events can give you the largest amount of Trick-or-Treat Bags if you are able to tag the majority of the enemies. They all have very low health and spawn at approximately the same location, so tagging them is going to require the use of constant cleave attacks on their spawn point.
Note that the type of door (Mad King Door or Bloody Prince Door) doesn't have any effect on whether or not a door will spawn a boss event, veteran event, or normal event. It does have an effect on which enemies the door can spawn, though.
Boss Events
Boss events can only be spawned from one specific door. Their exact locations are marked on the GW2 wiki page of their bosses. If you are interested in only getting bags, it may be in your best interest to navigate the zerg away from these doors, entirely. However, they are achievement-related, so people will want to do them at least once before the holiday is over.
Veteran Events
These events go by much quicker than Boss Events, but since they are so easy, I recommend also killing nearby enemies after you've tagged the Veteran.
Mad King Door
- Candy Corn Elemental
- Gargoyle
- Glow-in-the-Dark Spider
- King-Sized Candy Corn Elemental
- Plastic Spider
Bloody Prince Door
- Mummy
- Skeleton
- Rebel Lunatic
Normal Events
These are the events that you are most interested in, as you'll get the most kills and the most loot.
Mad King Door
- Bite-Sized Candy Corn Elemental
- Candy Corn Elemental
- Gargoyle
- Glow-in-the-Dark Skeleton
- Glow-in-the-Dark Spider
- Plastic Spider
- Small Plastic Spider
Bloody Prince Door
- Mummy
- Rebel Lunatic
- Skeleton