Do the Monster Bash Trophy in Costume Quest
Do the Monster Bash
Get the jump on 10 different monsters by pail bashing them to initiate combat.
How to unlock Do the Monster Bash
You'll first be able to do this after you trick or treat every house in the entire first area of the neighborhood. Meaning you'll need to knock on the door of all 20 houses. Once that's done the main gate that your sister was initially thrown over will open up. Follow down that path and you'll see an enemy out in the open with his back turned. Make sure that you don't walk into his line of sight and sneak up behind him. Hit him with your trick or treat pail by pushing . This will initiate battle and start the enemy off with a nice chunk of damage taken. From here on out every area you go to will have enemies out in the open for you to sneak up on. If you see that they've taken damage at the very start of the battle you'll know that you've done it right. Do it 9 more times to obtain the trophy.
To make this trophy easier you can wait until you get the ninja costume. This costume's special ability allows you to move unseen and walk right out in front of enemy without having them see you. Use this ability by pressing . You can use it to your advantage by holding and then walking around behind the enemy giving you a 100% chance of success. To find out how to get the ninja costume read the description to Dressed to Quest.