In what I expect to be a rough order of ascending difficulty:
- Out With It: If you can make yourself sick on Halloween candy in real life, managing it ingame isn't too much of a stretch. Tricky Treats are "drops" from Headless Horseman kills, and you'll get dozens of them from little pumpkins you can click after a kill.
- The Savior of Hallow's End: These were easy and fun quests to do last year, so unless Blizzard's changed them significantly, they should be quick. More importantly, doing one will also reward you with a Weighted Jack O' Lantern, and you'll need at least 10 of these to do the Check Your Head Achievement listed below because the Jack O' Lanterns are single-use items.
- Bring Me the Head of...Oh Wait: The Headless Horseman isn't a very difficult fight -- the real difficulty, as with Brewfest, is going to be finding people able to summon him after your group's exhausted its own summons. But killing him once for this Achievement isn't hard at all.
- Tricks and Treats of Azeroth: This isn't hard, but it will require a certain amount of time invested running all over the place to visit candy buckets. Doable as long as you've got an hour or two to yourself, or if you can knock off a few buckets per day.
- Check Your Head: This one won't be tough as long as you've done the Savior of Hallow's End quests enough to get 10 Weighted Jack O' Lanterns, or gotten them as drops off the Headless Horseman.
- G.N.E.R.D. Rage: I'm not positive but I think these are a new addition to the holiday; I don't remember them from last year and I can't seem to find much information on them. I'm guessing they'll be a random drop from Treat Bags you get from innkeepers, or from the Smashed Pumpkin Loot you get at the end of doing the Savior of Hallow's End quests. If so, 50 Honor Kills shouldn't be too hard as long as you're hitting the BG's regularly -- the only trouble will be getting enough G.N.E.R.D. candy to re-buff yourself after a death (unless the buff lasts through death, which I doubt it does).
OK. All of these are reasonably easy and will just require some time invested, and a 5-man group for the Horseman. But this is where things get a little trickier, and far more dependent on luck.
- The Masquerade: This is the easiest of the three harder sub-Achievements, because the wands involved have multiple charges. The wands are random drops from Treat Bags and Smashed Pumpkin Loot, but there's a pretty good chance that, if you're going for this Achievement with a few friends, between all of you you should be able to cover the wands needed. So, while there's an element of chance involved, Hallow's End spans nearly two weeks and odds are very good you'll run across each wand if your posse is diligent.
- A Mask For All Occasions: This is going to be a matter of luck, pure and simple. The masks are BoP items randomly looted from the treat bags given to you by innkeepers, and you can't trick-or-treat more than once per hour. You can also occasionally find them from Smashed Pumpkin Loot, but it's entirely possible (and, as a matter of fact, very likely) that you'll get a lot of repeats and there'll be a few masks you're missing by the end of the holiday. The only thing you can do to increase your chances of getting each mask would be to trick-or-treat every hour you can, and do the Savior of Hallow's End quests as much as possible.
- Sinister Calling: This is where you need one hell of a lot of luck, unless Blizzard changes the abysmal drop rate on the Sinister Squashling. Wowhead lists it as a 2% drop, which I can well believe after killing the Horseman dozens of times and never seeing it last year. You'll also need a Hallowed Helm for the Achievement, although the drop rate on that is considerably better at 9%.
So, in summary, if you really want this title -- do the innkeeper trick-or-treating and Savior of Hallow's End
quests enough to get 10 Weighted Jack O' Lanterns,
and as many chances as possible at the flimsy masks and costume wands. That will cover all the "drops" you need to worry about outside of the Horseman event. Beyond that, it's a lot of running around and then just prayer once you've actually killed the Horseman. Hallow's End runs from October 18th (this Saturday) to November 1st, and don't forget Blizzard's penchant for ending events at midnight on the last day (i.e. as October 31st becomes November 1st, that is). Good luck!