You can get this costume after win agents these guy in North Plateau.
1. Christmas Trivia King
Answer 1,3,2,3,1,2,2,1,2,2,1
2. Ordinary Trivia King
Answer 1,3,2,1,3,1,1,2,1,2,3
3. Winter Trivia Champion
Answer 2,1,1,2,1,2,2,2,2,2,3
(https://i.imgur.com/eJaRkgh.jpg)(https://i.imgur.com/RV3BUli.jpg)(https://i.imgur.com/mbsqmih.jpg)
(https://i.imgur.com/RBmk8jT.jpg)