Darci Scott is one of Claire's best friends, and also the person behind the mole costume. Darci appears with Mary Wang throughout the first episodes as two of Claire's closest friends, up until the point that she begins absconding them to hang out with Jim and Toby. Unlike Mary, Darci doesn't realize that Claire is now a Trollhunter, alongside Jim and Toby. She seems to support Jim and Claire getting together, as referenced by her frequent asking if Jim asked Claire to go to the dance with him.
In Party Monsters, they think that Claire is throwing a party without them, which was actually thrown by NotEnrique, who invited the other Trolls of Trollmarket. Thankfully, Claire prevents them from finding out about this secret world, though they unwittingly mingle with the Trolls at the party, who she and Mary believe to be college students. By the end of the episode, their friendship is rekindled and Darci believes that Claire is secretly dating a college guy, but won't tell because she's afraid of breaking Jim's heart. However, Mary doesn't think so and believes that there is something even bigger going on and is determined to find out what.
She may have started a relationship with Toby, as of A Night to Remember, when it is revealed that she is the mole mascot that Toby has become enamored with, as she was the only girl in school who wanted him to ask her out, but she couldn't because Toby was too busy trying to ask other girls.