"A Deathday Party? I bet there aren't many living people who can say they've been to one of those - it'll be fascinating!"
-- Hermione Granger (CS8)
A Deathday Party is held on the anniversary of a witch’s or wizard’s death. Sir Nicholas de Mimsy-Porpington celebrated his 500th Deathday on Oct. 31, 1992. Harry, Ron and Hermione were the only living guests. The rest of the guest list were hundreds of Nick’s ghost friends including the other Hogwarts house ghosts, Peeves, Moaning Myrtle, the Wailing Widow from Kent and Sir Patrick Delaney-Podmore and his huntsmen from the Headless Hunt (CS8).
The party was held in one of the “roomier” dungeons. The passageway leading up to it was decorated with jet-black taper candles. The dungeon had a chandelier with blue-flamed candles overhead and an icy blue spotlight on the podium. Because of the large number of ghosts congregated the dungeon was very cold, “like stepping into a freezer”. An orchestra of 30 musical saws provided quavering music which the guests danced to. A long table covered in black velvet was laid out with rotting food including a large grey cake in the shape of a tombstone. To Nick’s dismay, Sir Patrick Delaney-Podmore failed to believe Harry Potter when he told him that he found Nick “frightening”. Then the Headless Hunt began a game of Head Hockey during Nick’s speech.
Harry, Hermione, and Ron stayed as long as they had to in order to be sociable, then fled, hoping to catch the dessert course of the Halloween Feast in the Great Hall.
Other guests described are a group of nuns, a man wearing chains, a knight with an arrow sticking out of his forehead, and a portly ghost who walks through the food in an attempt to taste it (CS8).
The term "death day" can be found in Old Icelandic, dauðdagr, and Northumbrian, deohtdaege (OED).
The Deathday party is a ghostly parody of a birthday party, but it could also be linked to many ancient cultures where Halloween was known as the Day of the Dead. It was said to be the night of the year when the souls of the dead returned home, so it seems fitting that this is the date when hundreds of ghosts from all over Britain converge at Hogwarts. --RP
Rowling wrote on her original website (JKR):
In the first draft of 'Chamber of Secrets', Nick sang a self-penned ballad explaining how his head had (nearly) come off. My editor was not very fond of the song and so I cut it. However, for those who are curious, here is the story of Nick's decapitation in his own moving words.
It was a mistake any wizard could make
Who was tired and caught on the hop
One piffling error, and then, to my terror,
I found myself facing the chop.
Alas for the eve when I met Lady Grieve
A-strolling the park in the dusk!
She was of the belief
I could straighten her teeth
Next moment she'd sprouted a tusk.
I cried through the night that I'd soon put her right
But the process of justice was lax;
They'd brought out the block, though they'd mislaid the rock
Where they usually sharpened the axe.
Next morning at dawn, with a face most forlorn,
The priest said to try not to cry,
"You can come just like that, no, you won't need a hat,"
And I knew that my end must be nigh.
The man in the mask who would have the sad task
Of cleaving my head from my neck,
Said "Nick, if you please, will you get to your knees,"
And I turned to a gibbering wreck.
"This may sting a bit" said the cack-handed twit
As he swung the axe up in the air,
But oh the blunt blade! No difference it made,
My head was still definitely there.
The axeman he hacked and he whacked and he thwacked,
"Won't be too long", he assured me,
But quick it was not, and the bone-headed clot
Took forty-five goes 'til he floored me.
And so I was dead, but my faithful old head
It never saw fit to desert me,
It still lingers on, that's the end of my song,
And now, please applaud, or you'll hurt me.