Treasures of Aht Urhgan Mission 22
Shield of Diplomacy
In the Mission 21 cutscene, Naja orders you to the Navukgo Execution Chamber. This is a BCNM that can be entered through D-8 of Mount Zhayolm.
Enter the area for a cutscene, and then head into the burning circle. There is no level cap for this fight, but like all BCNMs, only one full party (six players) may join.
You'll be fighting a Chimera-type NM. It has about 15,000 HP and does AOE damage. During the fight, Karababa (the Windurstian ambassador) will join you.
Defeat the NM for another cutscene.