I did Harry Potter. Including:
Invitations were scrolls delivered by owls (white balloons with pipe cleaner feet and Sharpie details, tied to people's door handles)
Two massive white sheets painted with a Hogwarts doorway and brick wall respectively. Hidden seam down the middle for running through the brick wall.
Treasure hunt through the Chamber of Secrets and beyond (fake snakes and spiders) and then through a giant string web complete with Aragog and babies. Final thing to do was smash a Papier mache Voldemort head full of golden snitches (Ferrero Roche with wings)
Printed Ford Anglia and Nearly Headless Nick onto tracing paper and put in the windows so the light shone through them
Sign across the stairs saying the third floor corridor was out of bounds etc
Used old toilet rolls painted white with reusable battery powered tealights to make floating candles on translucent thread. Strung up round the dining room
All food was HP themed including Hufflepuffs (wotsits) and Bertie Botts every flavoured beans, homemade chocolate frogs, butterbeer and so on.
Dobby's grave in the back garden
Games like Pin the Nose on Voldemort and HP Would You Rather
Have You Seen This Wizard photo booth with props
There was loads of stuff. I'd never done a party at home before and a couple of dd's friends were moving away so it was a big celebration in many ways.