Tiny Tina's Assault On Dragon Keep: Dark Souls easter egg
The "Lost Souls" side quest contains many references to Dark Souls. An undead hero named "Crestfallen Player" is waiting near a bonfire and states that he's died "eighty times" and another player keeps invading his game to steal his souls. Once the souls are retrieved a glowing red knight named "-=n00b_killer=-" will appear. Kill him and the Crestfallen Player will say that "-=n00b_killer=-" repeatedly backstabbed him while he drank from his flask. Once the side quest is over, he says "It can be hard out here on Pandora. You'd better hold onto your humanity as best you can."