There is no shed, but there is a farmhouse in Snoopy's Flying Ace adventure. When you arrive at the farmhouse, get the mask from the scarecrow and wear it. Now when you knock at the door, you go inside and it is Violet's party.
No. And that is not how to get a costume for the Island's purposes. Ctrl + Shift + P toggles the "pumpkin head" jack o'lantern on the Costumizer. On Great Pumpkin Island, you have to get the costume that is provided on the island. At the end of Snoopy's Flying Ace adventure (dodging the searchlights) you arrive at a farmhouse. There is a mask on the scarecrow there. Get it and wear it when you knock on the door.
Go back inside and give it to Linus.
There is no pigeon on great pumpkin island.
The pumpkin patch is to the right on Great Pumpkin Island. It was the only area shown in the island preview.
It is at the end of Snoopy's adventure, which you start by knocking down his goggles from the tree with the football. After eluding the spotlights behind the chimney, jump down and go right and you will see a mask on a scarecrow. Wear it and knock on the door and you can go inside.
There are no buildings or upper rooms on Great Pumpkin Island.
Snoopy's goggles are up in a tree after the Football scene. To get it down, use the football. After the adventure, you will reach the farmhouse and a scarecrow. Take its mask to wear for the party (you need to wear it, at least temporarily, to enter the farmhouse, which is the party at Violet's house).
The name of the island is Great Pumpkin Island. See the related question below.
you wait for the great pumpkin!
At the very end, there is a mysterious figure in the pumpkin patch!
There is no potato farm on Great Pumpkin Island.