Grabbed by the Ghoulies Available Cheats:

Hidden FMV seqence
Complete Challenge #21 to unlock the "Original Promo Movie" and "Deleted Scene - Crivens Gives The Chair" options in the replay storybook.

Concept Art
Get a Platinum Medal in Challenges #1, #3, #5, and #7 to unlock concept art pages.

Mini-games
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