Full list of all 20 Costume Quest achievements worth 250 gamerscore. It takes around 6-8 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 15 achievements worth 200 Gamerscore, and there is 1 DLC pack containing 5 achievements worth 50 Gamerscore.
Finished the game!
Completed all Quests in the game.
Collected all Battle Stamps.
Used every Costume Ability in battle.
Acquired the Pumpkin Costume.
Collected all Creepy Treat Cards.
Won all prizes in Bobbing for Apples.
Defeated Metxel in battle.
Used the Robot Costume to Boost off of 15 different ramps.
Acquired 5 Costumes.
Won the Autumn Haven Mall Costume Contest.
Collected a total of over 4,000 candies.
Got the jump on 10 monsters.
Defeated BoJonn in battle.
Defeated a monster in combat with a friend by your side.
Defeated Araxia in battle.
Completed all quests in Repugia.
Acquired the Eyeball costume.
Used the Pirate hook on 5 unique ziplines.
Found the mysterious visitor in the cliffs of Repugia.