Act 2 Quest 2: The Horadric Staff - Diablo 2
Quest Location: All over Act 2
Quest NPC: Deckard Cain
Quest Goal: Collect the pieces to the Horadric Staff & Assemble it
Reward: Access to Duriel & Act 3
Flag: This is one of the quests you must complete to reach Act 3
The Horadric Staff is the most important quest of Act 2 and it won't be completed until you're standing right in front of the final bosses room of Act 2. You can begin this quest multiple ways, the first of which is by bringing the Horadric Scroll you get from Act 2 Quest 1: Radament's Lair to Cain in Lut Gholein.
If you don't begin the quest this way it'll begin naturally at some point early on during Act 2 when you enter one of the zones or pick up an item involved with this quest. Basically what you need to do for this quest is to go to different dungeons throughout Act 2 and pick up all the key items that are required in reconstructing The Horadric Staff.
When you do this quest on normal you'll need to go to the Halls of the Dead for the Horadric Cube. On Nightmare and Hell you can skip this step since the Horadric Cube doesn't disappear once the quest is complete. Below is a quick list of where you can find each item and how to reach the zone in question.
How to reach each item:
Cube: Dry Hills > Halls of the Dead
Shaft: Dry Hills > Far Oasis > Maggot Lair
Amulet: Dry Hills > Far Oasis > Lost City > Valley of the Snakes > Claw Viper Temple
For those of you who need additional information about any of the above mentioned areas, below you'll find more detailed explanations.
The Horadric Cube - Halls of the Dead
You'll find The Horadric Cube inside the Halls of the Dead on the 3rd floor. The chest that contains The Horadric Cube is protected by a Super Unique by the name of Bloodwitch the Wild who is a cursed huntress. When you open this chest on Nightmare or Hell difficulty (assuming you kept your Horadric Cube from your Normal play through) nothing will spawn. If you ever lose your Horadric Cube and need to obtain a second one all you need to do is return to this location and open the chest and it'll spawn for you. Even if you are not currently on this quest.
Before leaving the Halls of the Dead be sure to grab the Waypoint on the second floor.
Staff of Kings - Maggot Lair
Let's start with a complaint, this is the worst dungeon in the entire game. The tunnels are so jam packed that it makes navigating this place extremely difficult and it also makes any class/build with abilities that don't fire in a straight line almost useless. Druids with Tornado and Paladins with Blessed Hammer are two good examples of builds that get totally screwed in these hall ways since they don't go in a straight line and hitting the wall cancels the ability.
If you're lucky enough to have an Enigma or any item with the ability to Teleport you, I highly recommend you skip everything in this dungeon and strictly just try to find your way down to the third floor where you can obtain the Staff of Kings. What you are looking for is the big ass bug on the third floor of the dungeon (pictured above). Defeat the bug and open the Golden Chest in its room to retrieve the Staff of Kings.
The Viper Amulet - Claw Viper Temple
This item is found on the second floor of the Claw Viper Temple and is guarded by a Super Unique by the name of Fangskin. Fangskin is typically Lightning Enchanted and on the higher difficulties him and his companions will be immune to Lightning. In order to obtain the Viper Amulet you'll need to defeat Fangskin then smash the altar in the center of the room to retrieve the amulet.
When you destroy the altar at this location you'll also complete Act 2 Quest 3: Tainted Sun.
Once you've obtained all three items required to make The Horadric Staff you'll want to pop open the Horadric Cube and place them inside before hitting combine. You'll now have the completed Horadric Staff which you'll need to place in the Orifice inside the Tomb of Tal Rasha at the end of Act 2 during the final quest, Act 2 Quest 6: The Seven Tombs (pictured above).
Placing The Horadric Staff into the Orifice will finally complete this quest and grant you access to Duriel, the final boss of Act 2.