The Seraph Merchant in Tiny Tina's Assault on Dragon Keep DLC is located in Flamerock Refuge
You can use Seraph Crystal to buy Seraphs such as the Consummate Florentine and Antagonist
Where to find the Seraph Merchant in Flamerock Refuge[edit]
1) Start from near the Inn, where Eleanor was standing
2) Go East past the "Inn" sign and towards the platform:
3) Turn left at the sign post:
4) Cross the bridge towards Streetwise Wharfs:
5) The Seraph Shop will be just ahead:
