Hallows Eve everyone (yes, Samhain is technically tomorrow)! To celebrate, I have a vampire-y name for you, and I'll have something a bit more Pagan-y tomorrow!
Marceline (pronounced either "MAHR-suh-leen" or "mahr-suh-LEEN") is the French form of the Latin name Marcella, which is the feminine form of Marcellus. It means "dedicated to Mars." Marcellus was originally a Roman surname and a diminutive of Marcus (some resources will say that Marceline means "little Marcus"). Saint Marcellus was an early Catholic pope.
A character named Marceline appears in the play and opera of The Marriage of Figaro (well, I assume she's in the opera too, I'm not sure exactly). She is a housekeeper and Figaro's mother, but she doesn't know that she's Figaro's mother. Marceline is in love with her son and is trying to marry him. Which is kind of weird.
But most people know this name because of Adventure Time. Adventure Time is technically a kid's show but there are a few jokes that children are just not going to fully understand. The humor is very weird (kind of like Ren & Stimpy) but that's why I'm a fan of it. Marceline the Vampire Queen is one of the main characters. If you've never seen the show and are concerned that this reference might be too scary, don't be. She only drinks the color red, not actual blood. Oh, and she also has a rock band.
Marceline actually spent a small amount of time on the American top 1,000 baby names. In the 1920s it ranked #785 and in the 1930s it lowered to #962. So the name is vaguely retro. The variant Marcheline has been getting some attention recently thanks to Angelina Jolie. She named her daughter Vivienne Marcheline after her mother Marcheline Bertrand. But there's still not enough interest for it to appear on the charts, though.
I'll admit that Marceline is one of my favorite names mostly because of Adventure Time. I don't see that as a problem. Sure, the show is very successful, but it's still not famous to the point that people outside the nerd-o-sphere will necessarily recognize the reference. Also, the name has a history beyond that. I've been seeing some Marcel's and Marcello's in America, so why not Marceline?