The name 'Costume Trunk' is a piece of irresistible wordplay: it's the Structure where Costumes for your Monsters are crafted AND it's a tree trunk. When the Costume Trunk is closed, there's even a THIRD version of 'trunk'! O, how it tickles our funny bone.
Collect Seasonal Cheer during a Seasonal Event and combine it with other crafting items to create Costumes that your Monsters can wear all year long! You can equip or unequip a Monster's Costume from its Info menu.