Watch Dogs 2: 15 Easter Eggs, Secrets & References You Must Find

3. "This Is Like That Secret Cow Level" - Diablo II

Just one line of dialogue, but when it's referencing something as beloved as this, it's all you need.

At a point in the story, when playing as Marcus during an intense infiltration, one of your team members will utter the phrase, "Nobody's gotten that far. This is like the secret cow level."

Said 'cow level' originated in Diablo II as an insanely hard bonus area also called the 'Moo Moo Farm'. You can find out how to gain access over here, but sufficed to say, Watch Dogs 2 doesn't - as far as I know - contain its own version of the villainous Cow King.