My main town has a horror theme but it still has a ways to go because I haven't played New Leaf in months and I'm still planning some stuff out regarding QR codes and paths. None of the villagers are particularly frightening since everything is so cutesy, but I did what I could with what Nintendo provides us with. For example, I have Pietro since people are afraid of clowns. Cobb since he sorta looks like a zombie pig and because his house has mad scientist equipment. Ankha and Lucky cover the ancient Egyptian and mummy aesthetic, and Stitches is kind of like a Frankenstein's Monster.
I have another town that is bird-themed. There's not a whole lot of QR code stuff to do with that, but every villager in the town is a species of bird.
Finally, I got another cartridge earlier this year so I could hopefully acquire the last few villagers that I really like but who I couldn't keep in the other towns. I plan to make it a magic themed town, maybe with a little bit of a circus aspect. Tiffany is the main villager I want for the town because of the whole magic trick where you pull a rabbit out of a hat and because she's my second favorite rabbit, behind Coco. The potential circus aspect came to mind since Marcel is another villager I really want to get for the town.
Unfortunately that final town hasn't come to fruition yet because I haven't had much time to play lately and when I do, I haven't been able to get Rover to suggest a decent map that I can live with. Too many ponds, or rocks in terrible places. It's kind of discouraging, but eh, someday it'll work out.