Hint: Remember to keep shifting planes, from material to spectral. When you run
into a wall, shifting from the material plane to the spectral and back again
is almost always part of the answer.

Hint: Everything is a weapon: bonfires, torches, spears, pipes, wall-mounted
spikes, shafts of sunlight, pools of water, and so on. You'll want to explore
every possible means of killing your vampiric and human foes, not only to get
from puzzle A to puzzle B, but also because it's fun!
                                        
Hint: The special abilities you gain from killing the big vampire bosses (there
are five) are necessary for completing the game. Every time you defeat one of
Raziel's brothers, try to apply the power you've gained to new puzzles--and to
the old ones that stumped you before.