Getting to Whimsyshire
Spoilers for Diablo III included, obviously...
The first ingredient is the Black Mushroom, an item that spawns in the Cathedral Level 1 in Act 1. Take the Waypoint to the Cathedral Garden and head inside. In a random room, youll find some large mushrooms sprouting up in the middle of the floor. Click them, and the first step is done.
Also in Act 1, Leoric Shinbone is right inside of Leorics Manor (because, naturally, there's where a skeleton king would leave his bones around). Swing inside and look for a fireplace if you can use the logs inside, theyll drop his shinbone. If not, reload and try again.
This ingredient brings you to Act 2. Head to the Waypoint Path to the Oasis and go straight down and hug the bottom wall. Theres an offshoot to the south with a shack, and theres a small chance there will be a man there. If hes not there, reload the game. If he is, save him from an attack event and hell let you into the Mysterious Cave. Inside the Mysterious Cave there is a chance that youll find a Mysterious Chest (not to be confused with any other named chests). If you find it, you have rainbow in a bottle. If not, reload and try again.
This is both incredibly easy and difficult to get. Head to the Bazaar in Act 2s main city and wander over to the merchant on the bottom left named Squirt. Shell sell you Wirts Bell for a pricy 100,000 gold. Small price to pay for Whimsyshire, though.
Load up Act 3 and head to the Fields of Slaughter (The Bridge of Korsikk Waypoint is the closest). Go straight up to the area and look for the Caverns of Frost if theres another cave in this area reload and try again. Inside there will be a typical assortment of enemies, but the Gibbering Gemstone can drop off of one of them. We had it drop from a random Rare (yellow-named) Chiltara, so keep an eye out for it since itll have a white name when it drops, making it easy to mistake for junk loot.
Staff of Herding recipe
Izual in Act 4 has a chance to drop this. Thats it, no tricks, no frills, just keep killing him. Weve seen it drop on the first try, and weve seen it drop on the 20th. Just get grinding.
Assemble the staff
Now, to use it
The description for the staff says that Only one bovine in all of Sanctuary could possibly have a use for this, and that bovines skeleton is in Act 1. Head to The Old Ruins and go south on Old Tristram road until you see a cows skeleton. Approach and youll meet the Ghost of the Cow King (which we all know isnt canon, since NO ONE actually killed the Cow King). Hell throw out some horrid cow-themed puns before opening the door to