Swashbuckler can work pretty well. As Flay pointed out, dark creepy dudes with rapiers fit in quite well in horror settings (and they don't have to be half vampire!
). Kurashu makes a good suggestion with pirate.
Really, if you figure on the bare bones of a swashbuckler as being a "lightly armored combatant who focuses on mobility and finesse", you have a lot
of options open to you. You can go anywhere from:
Personality could be anywhere from light-hearted to quite serious, really. You don't have to play a goofy slap stick character to run a swashbuckler.
Also, as far as the build is concerned, I'd suggest mixing in 3 or 4 levels of rogue and taking Daring Outlaw (from Complete Scoundrel). You'll likely want to find some magic that will let you sneak attack undead creatures if you're in a horror game.