Halloween 2006

The Halloween 2006 Event runs from Thursday, October 26 until Tuesday, October 31, 2006. It includes the return of Halloween collectors, the redecoration of Lion's Arch and Kamadan, and perhaps more importantly, the return of Mad King Thorn who will once again terrorize the populace with terrible jokes while at the same time rewarding them with special holiday treats.

This is from the game update that made changes for the event:

When the moon shines down on the Elona Like the eye of a ravenous drake

Keep a lantern close by and the darkness at bay For on this holiday night, they say

A spirit returns, pumpkin on head Wicked deeds (and bad jokes) will abound He’ll bluster and shout Spread chaos about ’till a banishment for his mischief be found

Heed my tale, ye brave heroes From lands north and south Listen wherefore I say: Bind your sanity close, lest you lose what you love most When the monarch of madness appears.

From Official Event Page

Mad King Headwear Gifts
The Mad King distributed two special headwear gifts during the event, Halloween 2005's gift was the Pumpkin Crown, for Halloween 2006 the gifts were a Furious Pumpkin Crown for people located in Lion's Arch, while people located in Kamadan were gifted a Wicked Hat.

Collectors

 * Ascalon City
 * Horseman Nurmangor collecting 3 Charr Carvings
 * Horseman Irimund collecting 2 Ornate Grawl Necklaces
 * Lion's Arch
 * Horseman Vulgamor collecting 3 Decayed Orr Emblems
 * Horseman Malfein collecting 2 Glowing Hearts
 * Horseman Sorcien collecting 1 Feathered Caromi Scalp
 * Henge of Denravi
 * Horseman Saralim collecting 2 Maguuma Manes
 * Horseman Darelum collecting 1 White Mantle Emblem
 * Kamadan
 * Horseman Naramor collecting 2 Mandragor Carapaces
 * Horseman Garthim collecting 3 Sentient Roots
 * Horseman Aramon collecting 3 Juvenile Termite Legs
 * Champion's Dawn
 * Horseman Jaysin collecting 3 Copper Shillings
 * Horseman Bishma collecting 3 Fledgling Skree Wings
 * Kodlonu Hamlet
 * Horseman Kronar collecting 3 Silver Bullion Coins
 * Horseman Vadir collecting 1 Chunk of Drake Flesh
 * Sunspear Great Hall
 * Horseman Maxilus collecting 2 Mandragor Carapaces
 * Horseman Nuher collecting 3 Sentient Roots

''Transmogrifier Tonic is currently only available through Horsemen Garthim, Bishma, Vadir, and Nuher in Elona as well as from Mad King Thorn. ''

Henchmen
The Mad King's Guards are actually Henchmen. You can add them to your party and take them to explorable areas.