Cardboard tube Reaver:
Pause game play as Kain, then press Up, Down, Left, Right, R2, L2, Triangle, 
Down, Circle. Your Reaver will be replaced with a cardboard tube (as from a paper 
towel roll).

Switching Reaver Alignment 
If you switch alignments while holding down the square button when your reaver 
energy is full, you can sucessfully change which spell you use without losing your 
full bar. 

Unlock everything
Just beat the game and save the info to your memory card then go to bonus 
materials to see them. Don't worry about finding the tomes, they are all opened 
when you beat the game.

Kain's tomes - found throughout Kain's journey 
Making of LOK Defiance - finish game and save to memory card 
Raziel's tomes - found throughout Raziel's journey 
Soul Reaver 1 - opening start new game 
Soul Reaver 2 - opening start new game