Andariel, the Maiden of Anguish, serves the Greater Evils, doing their bidding and biding her time until she may seize power in Hell for herself. In this game she's been summoned by Diablo and left behind to guard the Rogue Monastery, preventing any heroes from following him to the East. Characters must defeat Andariel to pursue Diablo across the vast desert to the town of Lut Gholeim.
Andariel is dangerous in close; she packs a solid melee attack, can sting with poison damage, and throws a wave of toxic clouds out in an arc that poisons anything in their path. She is especially deadly to minions, her poison damage draining their life very quickly.
Use poison resistance equipment and antidote potions when fighting Andariel, and use the terrain as well; the blood lake in the atrium outside her throne room can be an effective obstacle, and many a player has survived this encounter by running round and round it, giving their healing potions time to work against Andariel's deadly poison.