Key Takeaways
Halloween has always been the season where DIY enthusiasts get to show off their quirky skills, and people will actually appreciate it for once. If you happen to have a 3D printer (and why wouldn't you?) then you're already looking at a great head start to making this Halloween the best yet.
Masks and Costume Accessories
Masks are the cornerstone of many Halloween costumes, and printers with beds large enough to print wearable masks are commonplace now. Just do a search on sites like Cults and you'll find plenty of masks that you can print.
Even if your 3D printer is on the smaller side, it might still be big enough to print a child-sized mask, and don't forget that you can split models up in the slicing software of your choice and then physically glue the parts together. You can also change the mask's orientation to use vertical space, at the cost of more support material. In my experience, tree supports work well on the inside of the mask if you want to angle it on the bed to gain more space, but a lot depends on the specific mask design.
Apart from masks, there's lots of potential for accessories, like plastic weapons, crowns, jewelry, and anything you can imagine. You can make them yourself as well, if you know your way around CAD or sculpting software, but there are plenty of talented sculptors on freelancer sites that would make you a custom model to print if you really wanted something custom.
Glow-in-the-dark filament is awesome, and one of my favorite materials to print with. It's perfect for making Halloween stuff, and it's not much more expensive than regular PLA or ABS filament. I've also never had any special issues printing in glowing PLA, and you get colors beyond green with even rainbow glow-in-the-dark filament options.
The main downside of this material is how much it wears down printer nozzles. The typical brass nozzle most printers use will be kaput after just one roll of the glowing stuff, thanks to the hard minerals the filament is impregnated with. So budget for a new nozzle at the very least, and seriously consider switching to a hardened steel nozzle if you don't like the idea of frequently changing out the brass ones.
Creepy Decorations
Halloween is all about getting the right atmosphere and decorating your home and workplace with creepy and ghoulish objects, but if everyone's buying the same stuff from the same old local and online stores, things will get boring fast. If you look at 3D printing models available online, there's endless variation and creativity. Your bats and skulls don't have to look anything like your neighbor's, and with some paint and a little patience, you can do some truly unique and creepy stuff.
Custom Candy Buckets
Whether you want something to store candy in before doling it out, or cool buckets to send your little monsters out on the hunt for sweet stuff, there are so many cool 3D-printable buckets and bowls online it's hard to choose.
Cults
I've actually printed hundreds of buckets for various events, and while they tend to come out just fine, you really have to pay attention to the supports. In some cases, it's even best to print the bucket upside down on its rim, as long as your printer can handle the angles, you can get away with no supports this way. If not, the upright position is best, but you'll have to accept some imperfections on the bottom of the bucket where the supports make contact. Still, no one is looking at the bottom of the bucket!
It's a little ironic that an advanced tech gadget like a 3D printer would pair so perfectly with a tradition based on the supernatural, but in the spirit of the holiday, why not have a little ghost in the machine?