Decoration ideas for a costume ball setting?

I'm having a murder mystery party and it's about immortals going to their annual costume ball. I want the decorations to be awesome but I'm a teenager with limited funds. So any ideas?

Details:

1. i saw this awesome shower curtain at spirit. it was made so it looks like there was a serial killr behind it about to kill somone. get it.
2. is it like the classic 1920s or what? thats what i recomend! masquerade decorations! and dead bodies!