Hallow’s end begins today and we can now farm the Headless Horseman. The headless horseman is a mob that can be summoned in Scarlet Monastery, drops epics and need a 5man group. You also need someone with a daily quest to summon it. Considering that you have someone in the group with the quest, you should be able to farm it over and over (remember the 5 instances/hour limit).
The loot table and strat for him can be found HERE. Some people will want the epics, but I think that what most people wants is the Sinister Squashling and the Swift Flying Broom/ Swift Magic Broom.
You can find a guide to the Hallow’s End quests HERE.