Niro is a member of the Cult of the Snake who hangs out in the Satyr’s Tail with his associate Grecos and insulting the other patrons; though, as they are likely speaking theives' cant, it is difficult to know exactly what they are saying.
After the Oracle's Chosen made a bit of a bodge job of trying to find out who in the bar were agents of the Cult, Niro went to inform the Lady of Coins that Calliope was sneaking around. He was followed by Hippofilius and Helikaon, inadvertently revealing the Cult's hideout.