After completing a difficulty by killing Diablo (or Baal in Diablo II: Lord of Destruction), you can open a portal to the fabled Secret Cow Level back in the Rogue Encampment of Act I. However, you need to find some items before you can do so.
- Wirt's Leg
- One-Hand Damage: 2 to 8
- Durability: 66
- Mace Class - Speed -1
- +50% Damage to Undead
In the west corner of Tristram in Act I, Wirt's body can be found lying by the river, with a Carver Shaman and Carvers always nearby. Click on him, and his peg leg drops in a fountain of gold. Wirt's Leg requires 3x1 inventory space, and can only be picked up if one is not already equipped or present in inventory or stash. Ideally it should be picked up for the first time while completing the Search for Cain, although the portal to Tristram can (still) be found at the Cairn Stones in the Stony Field.
Before you use it to open the portal it can also be used as a weapon, like a club: it may have sockets, and it can also be imbued by Charsi after returning her Tools of the Trade. It can still be used to open the portal even after being modified in any way.
Wirt's Leg cannot be used to make Rune Words.
You should already have picked up a Horadric Cube while completing the difficulty: it can be found in the chest guarded by Bloodwitch the Wild on the third level of the Halls of the Dead under the Dry Hills in Act II, or it will drop from the second Super Unique Council Member killed in Travincal in Act III for any character that does not already have one in inventory or stash. It requires 2x2 inventory space.
Once you have any Horadric Cube, return to Act I and place a Wirt's Leg from that completed difficulty in it with a Tome of Town Portal, which can be bought from Akara. Once you transmute these, a red portal will be opened wherever you're standing in the Rogue Encampment: if you do so while standing at the exit to the Blood Moor, then the portal may open just outside and be labelled No Level Name rather than The Secret Cow Level, but it still leads there. The portal remains open until you save and exit.
Moo Moo Farm
Once you enter the portal you'll find yourself in the Moo Moo Farm, a level populated exclusively by bipedal Hell Bovines wielding polearms, which spawn in groups of 5-10. Due to their individual and group size, population density and the openness of the level, it's inadvisable to wander around gathering large herds unless you're capable of applying significant damage to multiple targets, or controlling crowds by altering AI or using stun length, freeze length, cold length, Slows Target and the like.
Champion and Unique Hell Bovines are normally virtually indistinguishable from normal or minion Hell Bovines, which is another reason to be alert. The portal also tends to open near, and sometimes inside, a corral containing the Cow King...
Only Hell Bovines can drop the Cow King's Leathers set (Cow King's Horns War Hat, Cow King's Hide Studded Leather and Cow King's Hooves Heavy Boots). Despite the name, these items can drop from any Hell Bovine, not just the Cow King himself.
The Cow King normally spawns in or around the south corner of the corral, which is similar in appearance to the stockade of the Rogue Encampment. He's accompanied by six minions in Normal, seven in Nightmare and eight in Hell. He's also Immune to Lightning in Normal (115%), Nightmare (140%) and Hell (165%). In Nightmare, there's 10% chance of him becoming Immune to Fire (100%) when Fire Enchanted, and the same chance of becoming Immune to Cold (100%) when Cold Enchanted. In Hell, there's ~18% (16/90) chance of becoming immune to each of the following:
- Immune to Physical (100%) when Stone Skin (and FE or CE not selected first)
- Immune to Fire (165%) when FE (and SS or CE not selected first)
- Immune to Cold (165%) when CE (and SS or FE not selected first)
The Cow 'King' always drops eight Stamina Potions upon death (among other things) but, although this completes this 'quest' (there is no Quest Log), players normally aim to kill everything in the Moo Moo Farm except the Cow King, since killing him prevents the opening of another portal to access the level again in that difficulty (even when they do not kill him themselves: this quest is completed for all players present in the level when anybody kills him who has not done so in an earlier game).
Although not as popular as in earlier patches, players still often run the Secret Cow Level due to the lack of any inherent immunity, even in Hell, and the high number of kills and thus drops possible in a short period of time. Since the Cow King is Immune to Lightning in every difficulty, characters specializing in lightning damage are recommended for clearing the level with little to no risk of killing him (Amazons with Lightning Fury and Sorceresses with Lightning Spells are popular choices; Zealot Paladins with Holy Shock, and Assassins with Lightning Sentry or Claws of Thunder, are other possibilities).
However, players who have already completed this quest can still access the level via a portal opened by another player who has not (they may also collect another Wirt's Leg, even though they can't open a portal with it). Players who have already killed the Cow King can also do so again without completing the quest for other players in the level. It's best for the opener of the portal to never enter it, since this ensures there's absolutely no chance of them losing this ability.