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.
Defeated a monster in combat with a friend by your side.
Use the Robot Costume to Boost off of 15 different ramps.
Get the jump on 10 different monsters by pail bashing them to initiate combat.
Win the Autumn Haven Mall Costume Contest.
Acquire 5 Costumes.
Acquire the Pumpkin Costume.
Use every Costume Ability in battle.
Collect a total of over 4,000 candies.
Defeat BoJonn in battle.
Defeat Metxel in battle.
Beat the game.
Complete all Quests in the game.
Collect all Creepy Treat Cards.
Collect all Battle Stamps.
Win all prizes in Bobbing for Apples.
Acquire the Eyeball costume.
Use the Pirate hook on 5 unique ziplines.
Complete all quests in Repugia.
Defeat Araxia in battle.
Find the mysterious visitor in the cliffs of Repugia.