These seem to be the general consensus....this is from a post Kiya made
Warrior:
Drink a shadow potion and wait until her Blind spell wears off, then attack. Even when you are blinded, area effect spells which do not need a target will do damage (Hell Spikes, Elemental Hail...). If you drink a shadow potion and use the warrior's spin attack near (but not directly on) a creature, you will hit it without turning visible. Freeze weapons are useful, too
Mage:
Do you have Curse? A few casts of that before switching the Elemental Hail will make the attack much more effective. You can drink a shadow potion if Josephine casts Blind on you, to wait for it to wear off. Area effect spells that do not require a target (Hell Spikes, Elemental Hail...) may not turn you visible (don't know, never tried), but even if they do, they will work when you are blind. Blind / Hell Spikes works well against Josephine, if you get her first, or survive until her spell wears off.
I killed what most people think is the toughest boss in the game (Josephina) in less than 3 seconds by doing the following:
Killing Josephina
4 quick curses (level 5), freeze (level 4), 4 leeches (level 5), one hellspike (level 5). if you can click fast enough, you should be able to beat my time.
If you have a spare skill point, level 1 of the survivor's Deadly Gift combined with a couple scorpion traps would make it an easy fight. You can run up the ladder after releasing them...
I take it not much of your equipment has a vitality bonus? Even as a warrior with only a single stat point put into intelligence, towards the end of the game I had over 500 magic points from equipment bonuses.
Survivor:
If you have a spare skill point, level 1 of the survivor's Deadly Gift combined with a couple scorpion traps would make it an easy fight. You can run up the ladder after releasing them...