Even though he intends to kill the characters, Nezznar is curious about them. Given the chance, he quizzes the characters at length regarding their identities, allegiances, interests, and goals. He files it all away in memory in the hope that someday he might find a use for what he learns.
Nezznar admits to being the Black Spider, and to using the Cragmaw goblins and the Redbrands to ensure that Wave Echo Cave remains his secret. He will say or do anything to put the characters off their guard, including promising to surrender or proposing cooperation against the monsters impeding his progress toward reaching the Forge of Spells. However, he betrays the characters as soon as they outlive their usefulness.