The event is easy for my paladin with shield bash.
The hardest part is actually to collect 3 keysets.
The event starts by killing 3 uber monsters, Lilith drops Diablo's Horn,Uber Duriel drops Baal's Eye,Uber Izual drops Mephisto's Brain.
To create a red portal to Uber Tristram, place Diablo's Horn, Baal's Eye, and Mephisto's Brain in the Horadric Cube, and transmute them while standing in Harrogath in a Hell difficulty game. A red portal will open, the fourth in that area if you've done them all in the same game.
It takes you to Uber Tristram, where the real fun begins.
Uber Tristram has the same layout as regular Tristram, though the entry portal appears towards the north of town, rather than in the far eastern corner. Scattered through the center of town are Uber Mephisto, Uber Baal, and Pandemonium Diablo (so named because Uber Diablo was already used in another bonus quest). They are massively harder than their usual act boss selves, boosted by new abilities and much higher hit points, defense, damage, and more. They are also able to summon minions at regular intervals, further complicating things for intrepid adventurers.
