- Estimated achievement difficulty: 3/10
- Offline: 18 
- Online: 0
- Approximate time: 4-6 hours
- Minimum number of playthroughs needed: 1
- Missable achievements: 1 [Hardcorn Mode]
- Does difficulty affect achievements No
- Do cheats disable achievements: No cheats
- Unobtainable achievements: 0
- Extra equipment needed: None
Costume Quest 2 is a continuation of the story from Costume Quest 1. If you've already played the first game, everything should be very familiar because most of the same game mechanics have returned in the sequel. There appears to be a lot of reused assets as well, so if you were expecting a brand new experience, you may be disappointed. That being said, if you enjoyed the first game, it's safe to say you'll probably enjoy this one as well.
The Costume Quest games are turn-based RPGs. If you haven't played the first game already, I do recommend it. It's a fun game and a pretty easy 200, with an extra 50 for the DLC. It'll also familiarize the story for you.
All the achievements can be done in a single playthrough. There's a few story related achievements, some random tasks such as collecting 4000 candies, and some achievements related to combat. Most of these can be done just playing through the game.
It's unlikely you'll need a guide at all if you're the type to explore everything in your games. None of the worlds areas are particularly big, so it's easy to find everything. A possible exception is Downtown Repugia because it's a little bit maze like. Just be on the lookout for secret paths and areas and you should be fine.
There is one missable achievement in this game - "Hardcorn Mode". This achievement requires you to fight every battle with the Candy Corn costume equipped. Make sure you always have it equipped on one of your party members at all times if you want to avoid multiple playthroughs. Even if you miss it, the game isn't terribly long, but it's still a pretty significant amount of time for just one achievement.
Aside from "Hardcorn Mode", all other achievements can be done even after completing the game. Just quit to main menu, load your save, and you'll be back in the place just before the final encounter. The sewers act as a hub for every area of the game. Use that to go back and finish anything you missed.
[XBA would like to thank bs000 for this Roadmap]