As with her other brothers, Daphne makes occasional references to Nigel. It is implied he became a fisherman and a womanizer along with his other brothers. It is once mentioned that his brother Billy would peek at him in the shower, suggesting he is perhaps better looking/built than the other Moon men.
In Roe to Perdition, Daphne tells a (possibly fabricated) story about how Nigel became obsessed with cash after receiving a coin form the tooth fairy and began punching people’s mouths to collect their teeth. He was said to have been expelled, became a thief, and was arrested.