This...sounds...amazing. When I first started reading your post I thought of all sorts of things. Then I kept reading and you have all the things I thought of and more!! Chainsaw guy is scary. Especially if he's chasing you. Being shot at is equally as scary, maybe even more so as it's harder to dodge a bullet than a guy running at you with a chainsaw. ( And I always think, when I go in a haunted house, or maze, or whatever, " what if some psychopath is in here, hiding out, actually killing people, for real, and noone really knows until the next day because there is so much blood, and gore and screaming going on that noone notices??" Ok, I just gave myself the creeps.
But the spider thing...if you had realistic spiders, I mean, the big, nasty, hanging from webs waiting to cling to your face spiders....that would be the scariest thing ever for me. Not scared in a fun way, either...scared in an, "I'm gonna die from a heart attack" kind of way....
That's an idea, set loose a lot of those awful thorny country wood spiders that love to make huge webs out in your corn field and watch everyone freak out.
No really, now that I recommendend this please don't do it! Those things are horrible!!! i'm just saying those are the scariest things ever.