Grey Griffin's first big project was in "The Grim Adventures of Billy & Mandy," in which she plays the character of Mandy between 2001 and 2007. Joined by her brother Billy (Richard Steven Horvitz), "Grim Adventures" is about how the two siblings are able to trick Grim (Greg Eagles) into being their servant. Grim is a manifestation of death, and he looks just like a stylized depiction of the Grim Reaper. While Billy is a ball of energy, Mandy is a bit more pragmatic and calculating, and the two definitely have somewhat of a tenuous relationship with Grim — they abuse his supernatural powers and use him to go on all sorts of extra-planar adventures.
Speaking with Pop Dose in 2010, Griffin was asked about her role on "Grim Adventures," and she said she enjoyed the experience — but it was tricky for her to get Mandy's voice just right. She added, "Kris Zimmerman ended up directing the series, but Collette did the pilot, so they both had a hand in getting the voice right. It was really hard! It was the hardest voice I've ever had to do, because I'm such an animated person. When they said, 'Too cartoony, make it more real,' I'm, like, 'But I talk like this! This is me being real!' I love Adam, the guy that created the series. Well, he goes by Maxwell Atoms, but his real name is Adam, and he's a really great guy."
