Act V of Diablo II ends with the battle against Baal.
Act V was added by the Lord of Destruction expansion. Its campaign follows Baal’s invasion of the barbarian homeland and leads players through snowy settlements, mountain passes, icy caverns, and the Worldstone Keep.
The act culminates in a confrontation with Baal, the Lord of Destruction, inside the Worldstone Chamber. Baal is one of the three Prime Evils, alongside Diablo and Mephisto. His defeat concludes the expansion’s main campaign, although Diablo II’s multiplayer and character-building systems continue afterward.
Act V is sometimes mistaken for Act IV because Act IV ends with the original Diablo II campaign and the defeat of Diablo. Baal’s appearance and the Mount Arreat setting belong specifically to the expansion’s added act.