Sup my Fellow Little Nerds! Here is a detailed walk-through on how to get into the D3 Secret Level called Whimsyshire!
You need several things: 1. Black Mushroom (Act I) 2. Liquid Rainbow (Act II) 3. Gibbering Gemstone (Act III) 4. Wirts Cowbell (Act II) 5. [Plans: Staff of Herding] (Act IV) 6. Leorics Shinbone (Act I)
Reminder: You can acquire these parts in any order. The guide is written in a chronological order for simplicities sake.
Here is a Pro-Tip: Get some friends to do this with you. For the RNG parts, run them individually until you encounter the chest/rare spawn you need, then have everyone join that game.
From this point on, I will assume that you have completed one play-through of the game so consider this a spoiler warning for any potential spoilers it may contain.
Part One: Black Mushroom
The black mushroom is located in Act I, in the Cathedral. I saw lots of places that said that it could spawn on any floor which I found to be complete bullshit. I watched many different videos and read several different guides and in each picture they were located in the exact same place in the exact same room on the exact same floor.
My recommendation is to start the quest “Return to Tristam” on Normal.
The following method is the one that I used to obtain the mushroom. Apparently you can find the mushroom on more than one layout as a rare spawn.
Take the waypoint to the Cathedral garden, go up to the first floor and stop. If you do not immediately see a large staircase that you MUST walk up in order to continue backtracking, then you do not have the correct dungeon layout for it to spawn. Town portal, Leave game, and resume again. Repeat until you see a large stair case. When you find it will be in a room shaped like this with two entrances. http://img221.imageshack.us/img221/3761/mushroomlocation.png (I snagged the image from a random page, no screenshots are mine). The mushrooms are a random spawn in the correct dungeon so keep leaving and zoning in until you get the right setup and explore until you find that room. Once you find THAT room, if it’s empty leave and do it again you won’t find it anywhere else. It’s impossible to miss when you see it, it looks like I giant growth in the floor.
ALTERNATE METHOD:
Repeatedly clear Level 1 of the Cathedral until you find the mushroom, it will be in a room somewhere.
Part two: Leorics Shinbone
The shinbone is located in Leorics manor. I forget the quest name, maybe the imprisoned angel or something. Anyway, take the way point to leorics manor (the room where you walk forward a bit and there is a balcony and glass windows and stuff. Back track until you are at the very start. If you start walking back to where you were there is a room to the right of the staircase . At the end of this room is a fireplace, the shinbone is a rare spawn in the fireplace. It will either be empty or have a click-able “burnt firewood” or something to that affect. Click it and loot your shinbone. You may have to repeat it several times as it also is not a guaranteed spawn.
Part three: Wirt’s Cowbell
If you go to the last quest of Act III zone in and back track to the starting area. Go to the top left region of the map with the starting way point and look for a vendor named Squirt. She will sell you Wirts Bell for 100k. You can also get Wirts Cowbell from Squirt in Act II. She’s in the market (near the sewer).
Part four: Liquid Rainbow
Take the waypoint to Path of the Oasis. Follow the map along the southern most border until you find a little path heading further south to a little clearing. Look for Zaven the Alchemist, who must be saved from Deathly Haunts. He is not always down there. If you save him he will open a path to a dungeon. You must explore this for a mysterious chest or a resplendent chest (as reported in the comments). The alchemist dude is a rare spawn, and the chest is a rare spawn within the dungeon. Good luck and happy RNG.
Part five: Gibbering Gemstone
Go to Act III, take the waypoint to the bridge of korsikk. Run through the field ahead of you and check the top left corner, bottom left corner, and bottom right corner of the map for Cave of Frost Level 1. Again, the dungeon is a rare spawn. Inside the dungeon on floor two, you may get a rare spawn creature named Chiltara. It will drop the gemstone. I’d recommend running this on normal running past everything until you get to the second floor, and fully exploring the second floor to find him. Another rare spawn within a rare spawn type deal. Happy RNG.
Part six: The Blacksmithing Pattern.
Rare drop off of Izual. Start at the third quest. Clear up to izual, which you will encounter during the quest The Prime Evil. I thought I started too far but you fight him right before diablo. This one is a pain in the ass unless your lucky, because killing the boss gives you a checkpoint and you have to unfortunately re clear the whole area completely and kill him again. I was lucky enough to get it my first try. But my friends were not.
Once you get all these items. Train the blacksmith with your pattern, and make the item (costs about 50k for the staff.)
Take it to Act I. Take the old Tristam way point and head to the left back to the Old Tristram Road (you must be on normal with this version of the staff). If you follow the map border down the side of the map you will see a ghost come out of a cow skeleton. Talk to him and he will open the portal. Have fun.
Nightmare, Hell, and Inferno versions of the staff.
In order to access Whimsyshire on a higher difficulty than normal you must first obtain the version of the staff as listed above. Once you have it you must go to Act IV on the next highest difficulty (you must be on nightmare to obtain the nightmare blacksmith plan). Take the way point to Bastion Keep, and head all the way to the right and find the healer. Next to him there should be a vendor that sells the plan for 1g. It may not be on them the first time so leave and try again.
The only reagent for the new stave’s are the one you already have and a large quantity of gold. As reported, the normal staff is 50k, nightmare is 200k, hell is 500k, and inferno is 1million.
