The party went well, although they found the pinata much earlier in the treasure horcrux hunt than they were supposed to (I just put it back and they were happy to keep looking for clues). Also, although most of the kids are Harry Potter fans, it turns out few of them have reached the last book and so the idea of hunting horcruxes didn't resonate so much (this didn't seem to bother them, though).
I had thought about making little cardboard or clay replicas of each horcrux that they would have to break in order to get the next clue out of the middle, but luckily I came to my senses and just printed out a really cool set of horcrux icons (which I think is ok for personal use only, but I hope to buy one of those cool shirts at some point, too) on to cardstock and cut them out. Clues on the back said things like "Start at the entrance to the Chamber of Secrets" (answer was taped to the faucet of the upstairs bathroom) and "Travel by floo powder" (answer taped inside the fireplace), but also at least one mundane one "Are you hungry?". That was possibly the coolest hiding place, though, because it was Slytherin's locket and I'd taped it to the bottom of a clear glass punch bowl which had thick orange punch in it. Took them ages to find it and Daddy had to be really obvious about ladeling more punch into their cups and tipping the bowl, but Mr. P caught sight of it at last and about screamed himself hoarse in the excitement.
Treasure hunts are fun. :)
The nagini pinata turned out pretty awesome, too. Cardboard box cut outs for the front and back, cereal box strips for the sides, and one thin layer of paper mache to hold it all together (I used a simple and cheap Internet recipe for the paste, the cook method), and then paint and tissue paper for decoration. The toungue is two pieces of cereal box, paper mached together and bent before drying. Snakey cool, yeah? Multi-day project, but not too onerous if you have some time. Shmoogie loved helping with the paste. Here's the full thing, hiding "in the Shrieking Shack".
I had had thoughts (thoughts can be so grand!) of making/getting a wooden sword for them to hit the pinata with, but they were playing with foam noodles at the time they found the pinata and were happy to beat with those for a while, which got them nowhere, of course, but they did have fun and no one got hurt. When it seem like we needed something more serious, I just walked out with a broom and announced it was THE SWORD OF GRYFFINDOR and, you know what? The were perfectly willing to play along.
The cake, always the chocolate cake from The Art of Simple Food, this time with whipped chocolate ganache filling and poured ganache topping, was the best ever. Whipped chocolate ganache. Cannot go wrong. (Also, shockingly easy: 1 cup chocolate chips, 1 cup heavy cream, melt together gently, let cool to about room temp, whip. Although professionally trained chef of my acquaintance says use a chocolate bar, they melt better than chips.)
Mr. P had had some ideas about decorating the cake, but as usual I just ended up writing happy birthday and sticking in candles because I couldn't cope with more. You could play this off as Harry Potter-esque because that's basically the cake Hagrid gave Harry for his 11th birthday, but no one asked, so I didn't have to. I think they were too busy eating chocolate cake with whipped chocolate ganache filling.
And... I think that's what I've got. Back to apping!