WoW Achievements — Browse All Achievements
Track all 8,600+ World of Warcraft achievements. Browse by expansion or category — Dungeons & Raids, Quests, Exploration, PvP, Professions, Reputation, and more. Sync your character to see completion progress.
Browse achievements from all expansions including The War Within, Midnight, Dragonflight, Shadowlands, and Classic. Find guides for Glory of the Raider, meta-achievements, PvP achievements, exploration, and more. Track your achievement points and completion progress via Battle.net.
Diablo's 20th Anniversary
There is no cow level.
Diablo's 20th Anniversary is a limited-time Feat of Strength achievement earned by learning the toy 
Twelve-String Guitar, which drops from The Cow King inside the Cow Level.
Find a Treasure Goblin
Treasure Goblins can be found throughout the Broken Isles, including just outside Thunder Totem, or you can kill the final boss of any 5-man dungeon (including heroic difficulty) to spawn one. Kill the Treasure Goblin before it finishes casting Escape Portal, then click its corpse to be teleported to the Cow Level in Duskwood.
Kill The Cow King
Inside the Cow Level, defeat The Cow King to receive the Twelve-String Guitar along with other event items. Learn the Twelve-String Guitar toy to earn the Diablo's 20th Anniversary achievement.
Combine Town Portal Scrolls
Do not discard the 
Scroll of Town Portal drops from the event — combining 10 of them with a 
Blank Diabolic Tome creates a Tome of Town Portal.
Tips
See the video guide for a visual walkthrough of locating the Treasure Goblin and completing the Cow Level.
The event runs from January 3, 2017 to January 11, 2017, so complete all steps before the end date.