Happy Birthday Diablo III! The game came out three years ago yesterday and an anniversary like this means a special event. This time it's a Cowpocalypse, and it will be a nostalgic one for all Diablo fans.
Effective immediately, we encourage all residents of Sanctuary to steer clear of the wilds. From dawn on May 15 to dusk on May 21, it is also recommended that you avoid entering any strange portals that may or may not lead to alternate planes of existence. This activity cud be potentially hazardous to your health and, in the opinion of this humble civil servant, is a veally bad idea in general.
...says the anniversary post.
This means PC / PS4 / Xbox One players who log in from 15 May to 21 May will most likely encounter special Treasure Goblins with Cow Level portals and will be able to slay some moo-mooing beasts upon entering them. It's not available for PS3 and Xbox 360 players though, they have got a 100 per cent EXP and Gold buff instead.
Blizzard made a special video for the event. It's well hidden on the anniversary's page: you have to click on the face above the menu:
Cows are not a new addition to Diablo III, but their spawn rate was ridiculously low. So it's worth logging in and finally slay them all like it's a nostalgic trip to Diablo II.