Friday the 13th's Jason
First on the list is one of the simplest yet scariest costumes out there. The infamous mask + tattered coat + bloody weapon combo will definitely get some of your party guests running out the door. Just buy the signature mask (or make your own) and borrow an outfit that's equally as creepy and you're good to go!
As a child, I was never really afraid of clowns unlike some people who have terrible phobias. But I was never overly fond of them either and as I grew up, I started seeing the creepy side of them. I would definitely have nightmares if a guy dressed up as a clown with blood dripping down his chin knocked on my door...
Okay, just writing about him is giving me goosebumps. Freddie from the Nightmare on Elm Street just might be the scariest character in film history. I mean he's able to hurt you IN YOUR DREAMS which means you have NO ESCAPE. Jeez, whoever created this character definitely wanted people to have insomnia.
Don't be misled by the fact that Chuckie was 3 feet tall in the movie because I'm sure a ton of people would run out screaming if you dressed up as this killer doll. Try a red wig, denim overalls, a colorful striped sweater, and some costume make-up if you're not able to buy a costume.
The thing about zombies is that I love them in movies and shows like Zombieland and The Walking Dead but if a zombie apocalypse happened in real life, I would be scared shitless. So if you don't want to spend money on an actual costume then why not put on some zombie make-up (with the help of one of those online make-up tutorials such as this one) and do your best zombie impersonation!