I know an easy way to defeat mephisto. I used a necromancer and a higher level bone spear. Mephisto is quite stupid and doesn't know what 'wall' means. So if you lure him into a room and you get out and go to the other side of the wall, he'll be attacking the wall with all his might. That way you can jump in through the door from time to time and send some spears on him. Another way is to lure him in the corner of one of the curvy paths in the middle of the lair, and he gets stuck there too! Then you only have to move in from the opposite side, cast some spears and get clear. It takes a long time but it's efficient. And if you got some damage there should be a health shrine somewhere in the room.

OMFG EVERYONE IS SO STUPID. THE BEST AND EASIEST WAY 2 KIll ALL BOSSES IS 2 HAV SUM1 RUSH YOU

Well, if you have some patience and if you listen, you will hear the Deckard Cain say '...although she was spawned in the burning fires of Hell, Andariel is not fond of fire..."

Now If you are a Necromancer, then I suggest that you use my technique, because is the easiest (for me, at least).

To defeat Andariel: Once you're in contact with Andariel, keep running away from her in little circles. Then, while in motion, summon up a golem (clay or blood, does'nt matter which). And then, while Andariel is busy attacking your golem, you sneak up and attack her from behind. There is a 75% chance that she will ignore you and only concentrate on the golem. Once your golem is dead, runn away from Andariel in little circles and repeat the sneaking process until she is dead.

Also, for higher chances of not dying, I recommend that you follow these two simple steps:

1) While in circles, create a Portal to the Roque Encampment, so when you are low in life, you just go home. Once accoplished, go to Akara and speak to her. Just by going to her, you are automatically healed in health and mana. Full orb. And even if you dont make it to the portal. Once you press escape and come back to life, the portal should still be there for you to go back. And don't forget to make another Portal once your old one is expired.

2) Since you will be running away from Andariel, she wil likely use poison spells to send towards you if you are not in close-combat. So I recommend having a 50% Antidode Potions and 50% Health Potions.

Now, about Duriel. He is really, I mean really, tough. I died like what, 40 times before I could kill him so for the Sorceress, Cold spells would be the most effective because cold spell do three things in your favour:

1. They freeze your enemy so it cannot move (This is especialy usefull because if Duriel gets close, with one strike, you're as dead as a rock.

2. It prevents him from healing himself while in cold spells.

3. It also damages.

With Mephisto, I suggest the same thing I suggested to Andariel except a little less Antidode Potions and a bit more Health Potions.

Diablo and Baal I can't tell you because I have not encountered them yet.

Good Luck