We have two parties planned as of this writing: Death Day Party and Yule Ball.
Ideas:
Floating candles; a great DIY video can be found on https://www.thesitsgirls.com/diy/harry-potter-floating-candles/
Have You Seen This Wizard poster station; a DIY photo booth can be found on http://www.papertraildesign.com/harry-potter-party-photobooth-easy-diy/, then I used HP Reveal (formerly known as Aurasma) to make the wanted posters come alive.
Pin the Head on Sir Nicholas; granted ... Sir Nicholas is "nearly headless" but it should be fun anyways!
Dementor decorations; an excellent DIY video can be found on https://www.youtube.com/watch?v=RlzRgSDcVj0
Dragon eggs; I used large foam eggs, sequins, and large head straight pins (it took 2.5 boxes -- almost 1000 pins to create!) but was worth it for how good it came out. (I had Year 2s make these during one of our meetings. I was worried that the boys wouldn't want to but that assumption was unfounded. They all enjoyed making them and they turned out great!) I used these as decorations for the Yule Ball as well.
Horcrux Hunt; I created a version of the Marauder's Map with riddles to help club members find the horcruxes hidden around the school; I was going to use actual objects but opted for stickers; all finishers get drinkable Felix Felicis.
Save Dobby; we are at a Catholic school so we will donate socks and hats to the Migrant Ministry and do a collection in Dobby's honor.
Triwizard Tournament; Task 1: find the hidden dragon egg (receive points based on how fast the plastic egg can be found and the riddle inside can be solved; Task 2: save "friend" from merpeople (how many army men can be fished off of carpet in 30 seconds); Task 3: master the maze (who can answer the most trivia questions correctly); Triwizard Cups will be awarded for each task.
I used mini-trophies and spray painted them white first, then I used light blue and silver acrylic paint. I found a dragon drawing online and resized it, then I used Modpodge to add it to the trophy bases. I used a silver pen to write Triwizard and outline the dragon. I also used blue glitter paint to line the inside of the trophy cups. Lastly, I added mini dragons (just like they got in the movie!)
These were made from sequins and A LOT of large-head straight pins. Be sure to start at the narrow end of the large foam egg and work your way to the other end. There is a tutorial at youtu.be/RtUWqbcjq44 .
I found a drawing of Nearly Headless Nick online that was already divided up into squares. I enlarged those squares onto a sheet of chart paper and used them to help me sketch the drawing onto the paper. I then drew his heads using the same technique onto white construction paper. I then colored everything using crayons after first outlining it using a black Sharpie.
I glued together antique keys and butterfly wings then strung them up with white string to create the effect; both items can be found on Amazon.