As well as other valuable rewards, the Triumphal Challenge battle passes will grant you a special resource: Trophy Coins.
These Coins allow you to purchase various unique rewards in the Triumphal Challenge shop, such as Dragon Orbs, legendary Captain fragments, Elite Summoning Scrolls, and other resources.
The most valuable reward you can obtain is a unique permanent City appearance. It is the most expensive item you can buy in the shop. However, each City skin you purchase grants you a permanent 5% bonus to your army's strength. It is worth noting that the bonuses to army strength that are granted by each unique City appearance stack. I.e., they remain in effect even if you change your City's appearance.