Development Hell is a secert area in the game. During the "A Shattered Crown" quest in Act I on the Nightmare or harder difficulty, select the part where you have to open the gate. Go to the Cemetery Of The Forsaken and check all the crypt names. There are three areas named Defiled Crypt you can enter, one of which has the quest goal. When you enter one of the crypts, there is a random chance it will instead take you to Development Hell. If none of the crypts take you to Development Hell, save and quit the game. Restart the saved game and repeat this process until one of the crypts are Development Hell. In Development Hell, the normal Risen Dead enemies are named after the Diablo III development team, with their descriptions being their job title. The game director, Jay Wilson, is an elite monster, and killing him grants the hidden Feat Of Strength achievement "Smash! Jay, Smash!" along with a Banner Sigil.
When entering an area that gives you a life potion or chest, make sure to collect them. Once done, leave the game and resume it. The place where you clicked on to get the previous potion will give you another potion every time. Note: There may not be always a chest. If this happens, leave the game and resume it. Most of the time another chest will appear and the treasure will vary from an item to gold, or both.
Play the Act I quest "The Legacy Of Cain: Explore Cellar" segment. Take the waypoint to The Old Ruins and go north, then east. Go down the cellar to come across a named mob (Captain Daltyn) and his minions. Kill him for at least one magic item and some coins. Loot the cauldron for at least one health potion. speak to Leah for quest completion experience and gold. A loot chest also appears 40% of the time. Exit and repeat. The great thing about this method is that the pathway never changes. However, you will keep hearing a Tristram Militia whining about how he promised to save Marko and he did not.
This level has cute monsters, gold and item drops, health orbs (which look like large pink cupcakes), random and elite bosses, and a baby's blanket looking mini-map. To access the hidden Whimsyshire level, you must have three special ingredients, and a plan to teach the blacksmith how to craft them into the Staff Of Herding.
This object must then be taken to the Cow King's Ghost, a spectral bovine found on Old Tristram Road, near the pit with the mysterious red glow in Act I. After a conversation with the Cow King's Ghost, the glow will change to a rainbow color, and it will become an active dungeon entrance. When you enter the secret Whimsyshire level, a Feat of Strength, Banner, and Sigil will be unlocked. As was the case with the Diablo II Secret Cow level, characters must have defeated that difficulty level to enter the secret level, which is about as difficult as Act 4. The location of the required items to create the Staff Of Herding are as follows:
Black Mushroom: Rarely found in a room in The Cathedral: Level 1 early in Act I. It is a interactive ground spawn called Black Mushrooms, but it does not always spawn. One way to farm for this is to load a later quest in Act I, and take the Cathedral Gardens waypoint, then proceed through Leoric's Passage to the Cathedral level.
Wirt's Cowbell: Wirt's Bell is bought from Squirt the Peddler in the Caldeum Bazaar in Act II for 25,000 gold. It is under the "Miscellaneous" tab.
Gibbering Gemstone: Randomly drops from Chiltara in Level 2 of Caverns Of Frost in Act III. It is in the Ballistae fight area. If you get the Ice Caverns exit out, try again. The mob is random.
Plan- Staff Of Herding: Drops randomly from Izual in Act IV on any difficulty.
After acquiring the four items listed above, open your inventory, and select the pattern to learn it. You can now craft it under the weapon section for 50,000 gold. After creating the Staff Of Herding, players can use it an infinite number of times. You can make a staff for each difficulty. They are excellent for farming blues and rare items. To make the Nightmarish, Hell, and Inferno versions, you can find the plans at Gorell the Quartermaster at the east corner of Bastion's Keep Stronghold. He sells the plans for different prices depending on the difficulty you buy it for after you have killed Izual in Act IV.