Mod Culture Achievement in Costume Quest 2
Upgraded 3 costumes
How to unlock Mod Culture
Each costume in the game can be upgraded to become more powerful in combat. Upgrades can be bought with candy from a shopkeeper named Shady. He'll follow you to new areas throughout the game so it's not hard to find him. Buy any 3 upgrades to unlock this achievement.
I recommend only upgrading the costumes you use the most so that you don't have to spend any more time than you need earning candy. You should also prioritize the Superhero, Wolfman, and Hot Dog upgrades because those are required to unlock the Solar System Costume and "Cosmonaut" achievement.