The Butcher (Multiplayer & Single Player)
Quest given by: Wounded Townsman
Go down to level two (the Dungeon) and look for a room with lots of dead bodies and blood all over the floor. Open the door, and an Overlord called the Butcher yells out "Ah, FRESH MEAT!" and charges at you. He is fairly easy to kill. When he dies, he drops the Butcher's Cleaver (Single Player only).
Curse of King Leoric (Multiplayer & Single Player)
Quest given by: Ogden
Go to level three. In Multiplayer, simply wander the level until you find him. In Single Player, find the Tomb Entrance and go in. The Skeleton King will boast about killing you. Pull the levers in the outer rooms to open the Tomb. Kill the Skeleton King first using spells — he can re-animate his skeletons and is very deadly in hand-to-hand combat. When he dies, he drops the Undead Crown.
Poisoned Water Supply (Single Player only)
Quest given by: Pepin
On level two, find the area marked "to a dark passage" and enter. Kill all the Fallen Ones, Carvers, Devil Kin, and three goat men inside. The water in the cave will change from yellow to blue, completing the quest. Return to Pepin, who gives you the Ring of Truth.
Ogden's Sign (Single Player only)
Quest given by: Ogden
Go to level four and find a Dark One called Snotspill — he will complain about some "big uglies" stealing his banner. Go around the corner and kill the overlords. The sign is in the chest. Return it to Ogden for the Harlequin Crest.
Garbhad the Weak (Single Player only)
Quest given by: Garbhad
On level four, find the Goatman called Garbhad. He asks for "protection" from the things in the dungeon. Walk a full screen away from him, then talk to him again. Repeat this until he gives you an item, then attacks you. Kill him for a second item.
Magic Rock (Single Player only)
Quest given by: Griswold
Go to level five — the Magic Rock will be sitting on a table. Pick it up and give it to Griswold for the Empyrean Band.
Halls of the Blind (Single Player only)
Quest given by: a book
After reading the book, a secret area opens up. Enter it and kill all the "Hidden class" monsters. Your reward is the Optic Amulet. The quest is complete when you have the amulet and all the monsters are dead.
Zhar the Mad (Single Player only)
Quest given by: Zhar
Talk to Zhar and he will give you a book to keep you quiet while he works. Take all the scrolls and books in the area. When you take the book from the bookcase, Zhar gets angry and attacks. Kill him instead.
Anvil of Fury (Single Player only)
Quest given by: Griswold
In the caves, look for a peninsula of land surrounded mostly by lava — that is where the Anvil of Fury is located. Kill the defending monsters and carry the Anvil back to Griswold. He rewards you with Griswold's Edge, a unique sword.
Valor (Single Player only)
Quest given by: a book
Take the bloodstone and place it in the altar. A room will open — go in and get another stone. Repeat the process. A hall will open containing Horned Demons. At the end of the hall is the armour Arkaine's Valor.
Chamber of Bone (Single Player only)
Quest given by: a book
Find the staircase leading to the chamber. Once inside, kill all the Horrors and Horned Demons. Your rewards are several magic items and the Guardian spell.
Black Mushroom (Single Player only)
Quest given by: Adria
Find the Fungal Tome in the caves and give it to Adria — she will ask for a black mushroom. Return to the caves and pluck one. Give the mushroom to Adria, who then asks for some of Pepin's elixir. Pepin wants a demon brain. Kill a demon and bring him the brain. By this point, neither Pepin nor Adria still wants their respective items — drink the elixir yourself for +3 to all stats.
Lachdanan (Single Player only)
Quest given by: Lachdanan
Go to level 15 and find the Golden Elixir. Give it to Lachdanan, who rewards you with the Veil of Steel and a random magical item.
Warlord of Blood (Single Player only)
Quest given by: a book
On level 13, the Warlord of Blood is guarding the stairs down with his escort of knights. Kill them all and receive the unique sword Inferno, plus magical armour and weapons.
Archbishop Lazarus (Multiplayer & Single Player)
Quest given by: Cain
Single Player: Find the Staff of Lazarus on level 15 and give it to Cain. Return to level 15 — a red portal will have opened. Inside is a teleporter puzzle with grey circles. Eventually you will teleport next to Archbishop Lazarus. After a short cutscene, he attacks alongside many hell spawns and two bosses: Blackjade and Red Vex.
Multiplayer: Lazarus is in the top-right corner of level 15, assisted by four Advocates, two Hell Spawns, Blackjade, and Red Vex.
Reward: Three magical items.
Diablo (Multiplayer & Single Player)
Quest given by: Cain
Use the Red Pentagram to descend to level 16. Open up Diablo's area by pulling the Skull levers around the perimeter. Kill Diablo and watch the ending.
