Melciah:
This ugly pretentious guy is beaten by jumping over the side parts of the gates on the left and right of his main room & holding the lever until he slithers his way under the raised gate, then close the gate on him, do this twice (once in both side rooms) He laughs at you if you try to hit him with anything,
then lure him into the cage in the centre of the room by jumping in it, then when he gets in there with you quickly jump out.
< -- This is one of the two rooms where you gotta slam the gate on Melciah.

He will be stuck in that cage so now go to the lever & turn it to kill him.
Inherited ability: Phase through Gates (only in the Spectral realm).

Kain (first encounter):
This smart(BEEP)s always materializes the furthest away from you, you gotta run up to him & swipe him with your claws,
you should be able to just make it each time.........just!
Inherited ability: The Soul reaver.

                                                    ^
Kain gives you the Soul reaver after you beat him, by smashing it over your head!?

Zephon:
Hit his legs when they go into the ground,
after you have done that to each of his legs hit his Abdomen to get an egg,
run with it to the flame-thrower in the hand of the killed human near the door,
now that the egg is on fire throw it at his head.

You gotta do this a few times to kill him,
Raz should automatically aim at Zephon's head.
Inherited ability: climb walls.

Throw inflamed eggs at him.
 
 

Turel / Morlock / Tomb Guardian:
The easiest boss to beat! Just beat him up like you would a normal enemy, but watch out for his projectile! Don't forget to throw him in the moat or blow him up with the soul reaver.
Inherited ability: Projectile.

Rahab:
Ability requirements: Projectile.
Use the projectile to shatter each and every window, try holding R2 & L2 to manually aim, or Raz will aim at Rahab automatically-----of course that won't do the slightest bit of good!
< - - - Don't try Mooning Rahab, it won't do a thing.

Inherited ability: Swim.

Light engulfs Rahab once you shatter all of the windows.
 
 

Dumah:
Make him follow you all the way to that big room with the gas furnace in it,
if he isn't moving towards you hit him with the projectile,
turn the wheel to turn on the gas,
then pull the lever on the other side of the room to fry him.
Inherited ability: Constrict.

<--Enjoy the mini-movie when you deep fry Dumah.
 
 

Kain: (the final encounter)
This battle gets harder each time you hit Kain.
After the first hit he goes to the second level of the room,
after the second he goes to the third & the third hit is the final.
*If you see him charging his weapon but you don't want him to hit you with it then use the projectile.*