[Bozos of Bones]

OK, from the top

Efreet
Electicity does miracles. Fire elementals are totally ineffective against Efreet because they are of the same element. Try using Fireshield Blue and pound with Cones of Cold and the like.

Dragons
First few are nothing, just an intro. The Guardian is something else. Try being prepared with Call Lightning and Static and then when he's there, pound away with Lower Resistance, Malison, Emotion: Despair and then with heavy artillery. He is immune to Acid, and is quite resillient to fire I believe.

Iyachtu Xvim?
Lower Resistance, and then spread the party, start hitting with heavy damage wide area spells like Delayed Fireball and Horrid Wilting.

High Level Undead
Turn Undead is useless in HoF. But Undead affecting spells seem to cut it. But I never had any trouble with them, just cleave through them like you do with any normal folk.

Driders
The game tells you, electricity. Geedle's Electric Loop is one of the best spells in the game, and here is where it shines.

Lost Followers
By far the hardest fight in the game. Way harder than the final one. Critical hits with bows, axes, fists and oodles of spells and summons really bite. Come prepared, come in force and when things look bad, Holy Word is your friend.