#1 Diablo’s Secret Cow Level
The cow level in the first Diablo game was one of the first myths I came across as a gamer who played games online. According to the myth, players had to perform a complicated series of actions involving the cows at the edge of town and eventually get a red portal to open up in the field, which lead to a secret dungeon teeming with demons that were unlike anything else in the game. Screenshots of this secret cow level were doctored in Photoshop, of course, showing the presence of the red portal, as well as monsters in the dungeon using assets unused by the game.
When Diablo 2 came out, it had an actual cow level that you could open by combining Wirt’s Leg with a Tome of Town Portal within the Horadric Cube in Act 1, which summoned open a portal that lead to a field filled with cow monsters and a Cow King. Diablo 3 followed up on this with a cow level in Reaper of Souls’ Nephalem Rifts randomly generated dungeon system. There was even a Cow King’s Hide in World of Warcraft, a blue item that dropped from one of the game’s many monsters.
Needless to say, Blizzard’s in love with the myth and continues to keep it alive with easter eggs in their various titles.