There are 12 Trophies that can be earned in this title.

Bronze

Battle Buds
Defeat a monster in combat with a friend by your side.

Binary Bouncer
Use the Robot Costume to boost off of 15 different ramps.

Do the Monster Bash
Get the jump on 10 different by pail bashing them to initiate combat.

Dressed to Quest
Acquire 5 Costumes.

The Last Gourdian
Acqure the Pumpkin Costume.

Downsized!
Beat BoJonn in battle.

Dozer Dodger
Defeat Mextel in battle.

Silver

Master of Disguise
Use every Costume Ability in battle.

Sweet Justice
Complete the game.

All Decked Out
Collect all Creepy Treat Cards.

They'll Be Worth A Lot Someday
Collect all Battle Stamps.

Gold

Mask-O'-Raider
Complete all Quests in the game.

http://www.ps3trophies.org/game/costume-quest/trophies/