Darkening of Tristam guide: Get your baby cow pet in Diablo 3
There is a new "secret cow level" well hidden in Diablo III's 20th Anniversary update that will surely convey some good, old-school fun. Hidden in Diablo III's 20th Anniversary Event is another secret cow level. The event takes you back in time to the old town of Tristam, the very first Diablo title back in 1997. It lets players explore into the dungeon to eliminate the Lord of Terror for the last and first time.
Unlike the original game, it is now possible to get to the secret cow level legend which was a fake back then in the original game and even get yourself a pet cow. Here's how to get your own pet cow according to PC Gamer:
Gather the Rotten Mushroom
Head into the dungeon and fight through each level. When you hit the first layer or two of caves (usually at level 9), search every corner for a bright white group of mushrooms that is labelled black mushrooms. Click to get Rotten Mushrooms.
Craft the Witch's Brew
Back in old Tristam, take the first right into the curved detour and you will find a cauldron in an old shack. Click on it and you will inevitably use the Rotten Mushroom to create the Witch's Brew.
Wake up Farnham
Take the Witch's Brew to the group of scorched buildings in the middle of town where you'll find a dead body called Farnham and use the potion to revive the ghost which will then give you the Drunkard's Debt item.
Wake up the Other Villagers
Take Drunkard's Debt to Ogden, which will in turn give you Garda's Letter. Take it to Pepin, he'll give you a Healer's Prescription containing schematics for a child's wooden leg. Take the schematics back to your blacksmith in the real world and he will let you make Wirt's Leg.
Craft and Undo Wirt's Leg
Making the leg won't cost you any materials except for a million gold. After crafting, dismantle the leg straightaway and you'll get the Map of The Stars.
Revive the Cows
Take the Map back to old Tristam. Look for the cows to the right of the witch's shack. Revive the cow in the order described in the Map (2,1,3 = middle, left, right).
Claim your Sweet Pet Cow
Given you followed all the steps correctly, then you'll access a secret level, containing the chest that holds the Royal Calf pet. According to The Escapist Magazine, the explanations of the event and the item, it appears that the player stealing the little calf is what caused the Hell Bovines to go all wild in the first place that will continue throughout the entire Diablo universe.
So there, you now have cute little calf worth cuddling!