Ero
Ero is an NPC that sells Muh shop exclusive costume eggs that has common, uncommon, and rare category using Costume Coupon (1000274) . He's located a 2F Main Office east end of the hallway (main_office 125, 293).
Every common costume costs 7 Costume Coupon (1000274) , while uncommon costume costs 15 Costume Coupon (1000274) , and finally for rare costumes, cost 40 Costume Coupon (1000274)
Costumes that Sero has to offer:
Be Lucky Egg Boxes
Monthly Rotation of Costume Eggs