MMOGuides: Diablo 3 Secret Pony Level - Whimsyshire

Try Googling The Staff of Herding, Black Mushroom, Leoric’s Shinbone, Liquid Rainbow, Wirt’s Bell, Gibbering Gemstone, Whimsyshire, Pony Land, Cow Land, Diablo 3 Secret Level – or any combination of the above – and you’re likely to find a hundred different posts that list a hundred different ways to find a hundred different items you’ll need to collect in order to access the secret level in Diablo 3: Whimsyland.

This is harder than it looks. I spent an hour last night walking around Bastion’s Hold looking for the plans for the Staff of Herding that were supposedly found near a merchant before realising that this information was completely incorrect. 
It’s a complicated process, but we’ve figured it out. In short, you need to build the Staff of Herding to appease the Ghost of the Cow King, who can be found along the Old Tristam Road in Act I. Doing so will grant you access to Whimsyshire – the secret level in Diablo 3.

This is, of course, much easier said than done. The Staff of Herding must first be constructed by collecting 5 rare items scattered throughout various acts in Diablo 3 – alongside then finding the Blacksmith Plans that will, when combined with these items, yield the Staff of Herding – and this must be done again on each difficulty, and will considerably more difficult (and more expensive) each time.
Note: Collecting these items can take a long time – don’t lose heart, they will drop eventually.
THE BLACK MUSHROOM

The first of the 5 items required to construct the Staff of Herding is the Black Mushroom, which can be found in the Cathedral Level 1 during Act I. This is a random spawn, so it’s not guaranteed that you’ll find it on your first run – though, you can easily run it over and over via the quest selection menu of the character screen. 
LEORIC’S SHINBONE

The second item, Leoric’s Shinbone, can be found in Leoric’s Manor during Act 1 (9. The Imprisoned Angel). This one’s a little trickier to find than the Black Mushroom as it’s hidden within a pile of Burned Logs in a fireplace that spawns somewhere within the Manor.
It’s been reported that the fireplace will always spawn; however, the logs will not. If you find the fireplace without the logs, begin Leoric’s Manor, either —– again by leaving the game and starting over. 
LIQUID RAINBOW

The third item you’ll need to acquire, Liquid Rainbow, is a little more difficult to procure than the Black Mushroom and Leoric’s Shinbone, as it can only be obtained during a rare event in the Path to the Oasis during Act II. 

The best way to find the Liquid Rainbow is to travel to the Path to the Oasis waypoint and head southeast until you find the Mysterious Cave. Here, sometimes, Zaven the Alchemist will spawn, triggering an event that will ask you to save him, where you’ll come across a Mysterious Chest that drops the Liquid Rainbow. 
WIRT’S BELL

The fourth,and easiest to obtain item is Wirt’s Bell, which can be purchased from Squirt the Peddler in Act II for 100,000 gold. 
GIBBERING GEMSTONE

The final item, the Gibbering Gemstone, can be obtained in the Cavern of Frost – a random dungeon spawn in the Fields of Slaughter during Act III. Only one dungeon can spawn in the Fields of Slaughter, and there are 2 possibilities: the Icefall Cavern and the Cavern of Frost. If you find the Icefall Cavern, restart your game to try again. 
Inside the Cavern of Frost you’ll find an Elite enemy named Chiltara. Chiltara does not always spawn, but when she does, she will drop the Gibbering Gemstone. 
THE STAFF OF HERDING

With the 5 items above collected, you can now begin your search for the Blacksmith Plans required to construct the Staff of Herding. These plans drop from Izual, who can be found during the Prime Evil phase of Act IV. 
If after killing Izual the plans do not drop, simply leave your game and begin Act IV ‘Prime Evil’  to try again.

With the plans and items collected, head to the Blacksmith with 50,000 gold to create the Staff of Herding. Once this has been completed on Normal Difficulty, the plans can be re-purchased (with the new difficulty included in the name) from the Quartermaster merchant for 1 gold; however, all items will need to be re-collected on each difficulty, and the 50,000 gold craft cost will be increased exponentially. 
Nightmare Staff of Herding – 200,000 gold
Hell Staff of Herding – 500,000 gold
Inferno Staff of Herding – 1,000,000 gold
THE GHOST OF THE COW KING

With the staff now constructed, you’re ready to meet the Ghost of the Cow King, who can be found near the Read Glowing Crevasse on Old Tristam Road during Act I. He will teleport you to Whimsyshire, the secret level in Diablo 3. Enjoy.