The Giant Gold Feather is an item in Banjo-Kazooie. It is located in the very last room before the final fight with Gruntilda in Gruntilda's Lair. To access it, you must unlock a Note Door that requires 864 notes to open. Collecting the Giant Gold Feather will instantly replenish Banjo and Kazooie's supply of Gold Feathers. It is not required for the final battle, but considering that Gold Feathers are in short supply and its proximity to the final battle, it is an immense help.