[Your Name Here] the Hallowed

Here's an entire guide to the Hallowed.

Trick or Treat
Walk up to an innkeeper. Talk to them, and trick or treat.

Bring Me The Head Of... Oh Wait
Kill the Headless Horseman, located in SM GY.

That Sparkling Smile
Trick or Treat, and obtain a toothpick. Use it.

G.N.E.R.D. Rage
Get a crap ton of GNERDs, a candy from, you guess it, trick or treating. Do a battleground.

The Masquerade
Ask around, people with wands will transform you.

Out With It
Vomit. Yes, eat a ton of candy, you'll vomit.

The Savior of Hallow's End
Go to Goldshire or Razor Hill. Complete the quest to defend the town from the Headless Horseman.

Rotten Hallow
Go to Tarren Mill or Southshore and pick up the quest. Find the raid, bomb the town. Simple.

Check Your Head
Get ten pumpkin heads from the Headless Horseman. Go do a battleground, and give ten people head. Damn it, that sounded perverted.

Sinister Calling
May the RNG be with you! Get the Hallowed Helm and Sinister Squashling. Drops from Headless Horseman. You can do it five per day, try to be lucky, or have friends do it with you to get your pet/helm.

Tricks and Treats of Azeroth
Major time-waster. Simply follow the list in the achievement to go around the continent. When you get to the inn in the certain city on your list, right-click a candy bucket. Do this fifteen billion times in every random town in Azeroth, and you win.

Simple as that. Good luck - and let's hope you won't have to spoil your November-ish winter joy with a trip to the dentist. Candy rocks in moderation.