For every five "Rare books" that you find, you will unlock a bonus mini-game at the mini-game screen. There are 100 "Rare books" in the game, which unlock a total of twenty bonus mini-games. There is one "Rare book" in every room of the mansion.
Get a Platinum Medal in Challenges #1, #3, #5, and #7 to unlock concept art pages.
Complete Challenge #21 to unlock the "Original Promo Movie" and "Deleted Scene - Crivens Gives The Chair" options in the replay storybook.
Successfully complete the game, and you can view the staff credits at the "Features" menu of the game.
Enter the options screen and enable the "Butler's Brew" option. Now if you fall in any room, you will be given an option upon re-starting that room if you want Coffee and Waffles. Press A to select "Yes" and you will have double health.
You can see various pictures and statues of Banjo-Kazooie's "Mumbo Jumbo" in the rooms of the mansion. Also, whenever you fight a "Ghoulie", listen. They often sound like creatures from Banjo-Kazooie. Additionally, every time you enter the kitchen where Ma Soupswill is located, look on the billboard near one of the kitchen's doors. You will see a picture of Banjo and Kazooie.
When you start a new game, look at the three books that are shown. One says "Rare" and the other says "Microsoft". If you look closely, you can see that when "Rare" books pages are turned, there are pictures of Banjo-Kazooie and Donkey Kong Country. In the "Microsoft" book, you can see an Xbox, an Xbox Live microphone, and other Xbox items.