ToA p230 for stat block

From his lair in the fane of the night serpent above the tomb of the nine gods, Ras-Nsi leads the Yuan-ti cult who seek the return of Dendar the Night Serpent to consume the universe.

His lieutenant Fenthaza has ideas that Ras-Nsi doesnt agree with.

Ras Nsi is weak with the death curse, but is out of touch with real world events he hasn't made the connection with its cause. Fenthaza is also actively blocking the flow of information.