(Please click through to Think Geek. They might be having a sale!)
Among Marceline's totally awesome powers: Stylish Magic Clothing. Even when she shape-shifts into a much larger form, her clothes either shift with her, or explosively tear apart but then magically return when she goes back to her humanoid form. It's unknown if she received this power from sucking the soul of a really cool and stylish previously-slayed vampire, but we're down with that explanation...