maybe i did something wrong, but i could kill azrael only with the help of three genies. i lost whole hp in 2 sec from his aura. can't imagine to kill him with paladin or rogue.
gabriel was 1000 times easier.

Gabriel? I don't recall ever fighting Gabriel...but then I played a "good guy". Perhaps it depends on your alignement?

Anyway, I took care of Azrael with Pillar of Salt, then proceeded to stab him to death with the sword Inquisitor (he lasted about 5 seconds). Didn't even have to resort to genies, and I had about 14 of the magic boxes sitting in my inventory =P

Seriously though, Pillar of Salt is very overpowered by the fact that it strips an opponent of all its natural defences and, in most cases, allows enemies to be one-shotted.

i had pillar of salt, but didn't use it for last boss.
you can fight gabriel, when you decide to join the high priest at the end.