"....a moment later they had entered the Great Hall, where the Halloween decorations put Hermione out of their minds.
A thousand live bats fluttered from the walls and ceiling while a thousand more swooped over the tables in low black clouds, making the candles in the pumpkins stutter. The feast appeared suddenly on the golden plates, as it had at the start-of-term banquet." (PS10)
A special occasion at the school, with a magnificent feast and amazing decorations in the Great Hall.
Halloween Year One (PS10)
Where: Great Hall; to be continued later in the common rooms
Who: Hogwarts students & staff
Special/Strange guests: a Troll in the dungeons, interrupting the feast
Decorations: live bats fluttering from the walls and ceiling and swooping over the tables in low black clouds, making the candles in the pumpkins stutter.
Meal: feast appeared suddenly on the golden plates, a baked potato was the only food described before the announcement of the Troll and the vacating of the students from the Great Hall
Entertainment/strange events: Harry & Ron corner & knock out a twelve foot tall Troll in girls' bathroom, while rescuing Hermione; Snape discovered lurking on the third floor; Moaning Myrtle in the girls' third floor bathroom
Where: Great Hall; Death Day Party
Who: Harry, Ron, and Hermione attended Nearly Headless Nick's Death Day Party, which caused them to miss the Halloween Feast.
Entertainment/Guests: Giant jack-o'lanterns carved by Hagrid large enough to sit in; a "Troupe of Dancing Skeletons"
Strange Event : Harry heard the Basilisk inside the walls; Mrs. Norris the cat was found petrified in the Hallway, and a sign on the wall in blood said "THE CHAMBER OF SECRETS HAS BEEN OPENED. ENEMIES OF THE HEIR, BEWARE.
Where: Hogsmeade; Great Hall
Who: Hogwarts Students and Staff
During the Day: Hermione and Ron were allowed to go to Hogsmeade but Vernon wouldn't sign Harry's form so they brought him candy from Honeydukes. Snape brought Lupin a "smoking goblet" full of potion which worried Harry who thought it was poison. (Lupin turned up alive and well at the feast).
Decorations: Pumpkins, Bats, and "orange streamers which were swimming lazily across the stormy ceiling like brilliant watersnakes" (PA8)
Entertainment: The Hogwarts ghosts popped out of the walls and re-enacted Nearly Headless Nick's beheading.
Uninvited guest: Sirius Black, who slashed the Fat Lady's portrait during the feast, and broke into Gryffindor Tower trying to find Scabbers the rat (PA9). So Halloween turned into a slumber party in the Great Hall with "squishy purple sleeping bags" conjured by Dumbledore.
Halloween Year Four (GF16)
Where: The Great Hall with the Goblet of Fire
Who: Hogwarts Students and Staff, Durmstrang and Beauxbatons students and chaperones
Decorations: Bats and Pumpkins appeared in the morning just before Fred and George tried to cross the age line to put their names in the Goblet and were transformed into old men with beards.
Best costume: Hagrid tried to impress Madam Maxime with a "his best (and very horrible) hairy brown suit, plus a checked yellow-and-orange tie."
Surprise: Four names emerged from the Goblet of Fire instead of three, and even though Harry was too young for the Triwizard Tournament the magic was legally binding
Halloween Year Five (OP19)
No mention of a Halloween Feast, perhaps because of Dolores Umbridge who did not appreciate the students having fun.
"October extinguished itself in a rush of howling winds and driving rain and November arrived, cold as frozen iron..."
Halloween Years Six and Seven
No feast mentioned. Voldemort was frightening enough.
October 31st is also the anniversary of James and Lily's deaths and Voldemort's defeat.