We have two Grand Gathering planned for December.
The first is a Fireworks Cruise that begins at The Contemporary Marina with a dessert buffet and features Captain Hook and Mr Smee. After dessert we take a boat trip with a Pirate guide through Bay Lake, over the Aquaduct and then into the Seven Seas Lagoon. We anchor to watch the Fireworks over the MK and Peter Pan greets us when we return to the Marina at the CR. The cost is $35/$20 and is held Sun, Mon and Tues. Hours vary based on the Fireworks schedule. Days are subject to change.
The second is the International Dinner at Epcot. We have a Buffet Dinner with food from Morocco, Germany, Italy, Japan and China at The Odyssey. This features Characters and Entertainment. After dinner you have access to a VIP viewing area for Illuminations along with a dessert buffet. The cost is $60/$25 and is held Mon and Fri at 7:30. Hours and days are also subject to change.
I don't have info on the Good Morning Gathering or the Safari Celebration Dinner. The Grand Gathering phone # is 1-407-WDW-PLAN.