One of the really fun things about the "Mickey's Not-So-Scary Halloween Party" at Disney World's Magic Kingdom is that it has its own special shows, fireworks, and even parade. You'll see villains and ghosts, as well as more lighthearted fun. I've always liked it.
Maleficent of course is always quite delightfully villainous, but I've always had a bit of a soft spot for the Haunted Mansion, and so my favorite segment is always the section featuring hitchhiking ghosts and, of course, the creepy ballroom dancers.
Who's your favorite Disney villain?!