You are referring to Diablo II: Lord of Destruction (LoD) version 1.14d.
Since this was the final version before the remaster, it represents the "frozen" state of Diablo II's meta: diablo 2 lod 1.14d
The Pandemonium Event: Players collect Keys from specific bosses (Countess, Summoner, Nihlathak) to open portals to Uber Tristram, eventually earning the Hellfire Torch unique charm. You are referring to Diablo II: Lord of
Because it is the final legacy version, 1.14d is the base for several essential community tools: Frozen Orb/Blizzard — cold caster with strong crowd
The Skill Tree: The synergy system, introduced in earlier 1.10+ patches and finalized here, rewards specialization. Spreading points too thin is a recipe for failure in Hell difficulty.